GB2470461A

GB2470461A - Apparatus for monitoring attitude of a ladder

Info

Publication number: GB2470461A
Application number: GB1007174A
Authority: GB
Inventors: Ladderbox Uk Ltd; Geoffrey Hill; Robert Hill; Sean Quinn
Original assignee: Individual
Current assignee: Individual
Priority date: 2009-04-29
Filing date: 2010-04-29
Publication date: 2010-11-24
Also published as: WO2010125349A3; GB0907369D0; WO2010125349A2; GB201007174D0

Abstract

For safety, a ladder needs to be at a desired attitude in both elevation (75°) and from side to side (90°). A monitoring device is attached to the ladder using a cradle 86 which comprises a either a Hall effect sensor, two spirit levels mounted orthogonal to one another or a pendulum allowed to swing in two dimensions. This device has a microprocessor (figure 12 — 70) that drives a visual display (74) that shows the attitude of the ladder against a series of circular bands representing angles of deviation up to 1.5° degrees, over which an audible alarm (76) goes off. The device has a sleep mode which disables the device if it has been inactive for a predetermined length of time. Alternatively, the device can be carried by a person to monitor if the person is upright. Upon detection of the person not being upright a transmitter on the device uses a mobile phone to call out and let the receiver of the call know the location of the device.

Description

Apparatus for monitoring attitude This invention concerns apparatus for monitoring the attitude of a subject.

The invention has been developed for use in monitoring the attitude of a portable pole ladder or the like, although it is not limited to such use.

A pole ladder comprises at least one longitudinal stile with a plurality of lateral rungs secured thereto to provide footholds for a user. Most commonly, the pole ladder has a pair of stiles and the rungs extend between the stiles and orthogonally thereto. In portable form the pole ladder is in use leant against a wall or the like.

Safe use of the ladder demands that it be positioned at the correct attitude before use, both in elevation (against the wall) and from side to side (across the wall), and maintained in that position during use. In elevation, the standard recommendation is that the ladder be set at a nominal 75° angle of elevation, which in practical terms is translated into a 1:4 rule or one out to four up' whereby when the ladder is leant against a wall for use the foot of the ladder is positioned at a distance out from the wall which is equal to one quarter of the height of its top. For side-to-side safety it is recommended that the ladder be so positioned that the rungs are horizontal, as judged by eye, to secure verticality of the ladder across the wall.

Those skilled in the use of ladders will appreciate that it is not enough to position the ladder in advance. During use, the ladder may become out of kilter from the user, from the effect of gusts of wind (which may also unbalance a ladder positioned but not in use) or from movement of the item against which the ladder is leant -for instance if this is a tree or the like. It is * **** * therefore necessary to monitor the attitude of the ladder during use as well as in its initial positioning.

** There are things other than ladders which need to be monitored for attitude, and as noted above the present invention is not limited to monitoring the attitude of ladders.

Generally expressed, therefore, it is an object of the present invention to improve safety by monitoring the attitude of any subject which may constitute a risk if it departs from a defined attitude.

According to a first aspect of the invention there is provided a device for signalling deviation from verticality of a subject, which device comprises an inclinometer operative to measure attitude of the subject in two vertical planes and an alarm connected to the inclinometer to be automatically activated if said attitude in each plane is not within a preset range, characterised in that said device includes switch means manually operable to enable and disable the alarm alternatively.

Preferably the device includes an indicator operative to show when the alarm is enabled.

Preferably, too, the device includes test means whereby operation of the alarm may be tested.

The inclinometer may comprise two spirit levels respectively orientated in said two vertical planes. Alternatively the inclinometer may comprise a pendulum pivoted about two axes respectively orientated in said two vertical planes, in which case the inclinometer preferably comprises a Hall effect sensor, For convenience, the two planes in which attitude of the subject is measured are preferably mutually orthogonal.

The switch means, which may comprise a push button on the device, may be configured and arranged so that its operation requires it to be manually engaged for not less than a predetermined switch period.

The device may include sleep means operative to disable the device S.: automatically if it is left enabled but inactive for a predetermined working * S..** * period.

The device may also include smoothing means configured and arranged so that short-period movements of the subject do not activate the alarm. ***S * S S...

As will be understood from the introductory comments, the invention may be applied to monitoring the athtude of a portable ladder and to this end in a second aspect the present invention provides apparatus for monitoring the attitude of a portable ladder characterised in that said apparatus includes a device as indicated above operative to measure elevational attitude of the ladder in a first of said two vertical planes and side-to-side attitude of the ladder in the second of said two vertical planes.

Such apparatus may comprise a cradle for releasable attachment of the device to the ladder, which cradle is configured and arranged to be secured to the ladder in a setting such that when the device is received in the cradle said preset range includes an elevational attitude of 75° from horizontal in the first plane and a side-to-side attitude of 900 from horizontal in the second plane.

In this arrangement the device preferably displays attitude of the ladder against a scale showing said preset range. The scale may comprise rings about a datum of the preset range. These rings may define (a) a lock zone wherein the attitude of the ladder is within 10 from the datum, (b) a warning band around the lock zone, within which warning band the attitude of the ladder is between 1° and 2° from the datum and (c) an alarm band around the warning band, within which alarm band the attitude of the ladder is more than 20 from the datum. Each ring may be provided with means of illumination such as variation of brightness and/or flashing to signal the attitude of the ladder relative to the datum. This illumination may be accompanied by a sounder providing an audible indication of the attitude of the ladder relative to the datum. *..*

The invention is also of use in providing a warning if a person such as * a walker or climber has a fall or is otherwise unable to maintain an upright stance, to which end the, invention provides in a third aspect a device according to the first aspect of the invention with a carrier whereby the device may be carried by the person to monitor that the person is upright, **** * * **** ** I * * * * ** wherein said alarm is automatically activated if the person carrying the device ceases to be upright for more than a monitoring period.

This aspect of the invention may also include a transmitter operative automatically to transmit from the device a signal representative of the activated alarm. This transmitter may comprise a mobile telephone programmed to send an outgoing call automatically when the alarm is activated, and in this case the mobile telephone is preferably configured and arranged so that the person carrying the device may establish voice communication by way of said call -whereby in the event of an accident advice may be given to the person affected. The apparatus may also include means monitoring the location of the device, the transmitter being operative to include information identifying said location in said signal.

Other features of the invention will be apparent from the following description, which is made by way of example only with reference to the accompanying schematic drawings in which -Figures 1 and 2 show a portable ladder leant against a wall for use, respectively from the front and from one side; Figures 3 and 4 are views corresponding respectively to Figures 1 and 2, to an enlarged scale, and showing apparatus according to the present invention for monitoring the attitude of the ladder; Figures 5 to 7 illustrate, to a further enlarged scale, a form of the invention for releasable attachment to ladder, shown respectively from the front, from the side and from underneath; Figures 8 and 9 illustrate another arrangement for releasable attachment to a ladder Figure 10 illustrates the application of the invention to a personal safety * *.* S. * alarm; Figures hA, 11B and 12 illustrate a monitoring device according to the invention and making use of the Hall effect; and Figure 13 graphically illustrates the operation of a monitoring device S'S.

according to the invention for monitoring the attitude of a ladder.

Referring first to Figures 1 and 2, these show a portable ladder indicated generally at 10 leant against a section of wall indicated generally at 12. The ladder 10 is a pole ladder and comprises a pair of stiles 14 with a plurality of rungs 16 extending therebetween to provided footrests for a user.

The rungs 16 are orthogonal to the stiles 14.

To comply with health and safety standards, the user is required to set the attitude of the ladder 10 in two orthogonal planes. The ladder must be vertical as viewed from the front (Figure 1) -that is, it must not tilt to either side; and it must be set at a specified angle of elevation A (which for a ladder standing on horizontal ground is 75°) as viewed from the side (Figure 2).

Conventionally the user determines the correctness of the ladder's attitude by eye. Looking from the front, the user aims to set the rungs 16 horizontal. To set the angle of elevation, the user positions the ladder 10 so that the height h of its head lOa is four times the distance d of its foot lOb from the bottom of the wall 12.

There is inevitably some variability in the positioning of the ladder 10, especially when the user judges the attitude by eye. Viewing the ladder 10 from the front as in Figure 1, it is not easy to judge the horizontality of the rungs 16, especially if there are no visible courses of brickwork to provide a guide. Viewed from the side as in Figure 2, the relative dimensions of h and d may be inaccurately judged. For instance, in a situation where the head 1 Oa of the ladder 10 leant against the wall 12 (assuming this to be precisely vertical) is to be at a height of 4.Om, then the one out to four up' rule indicates that foot lOb of the ladder 10 should be 1.Om out from the bottom of the wall 12. But judged by eye, even an experienced user may put the foot iDa of the ladder 10 0.9m out from the bottom of the wall, giving an elevation * ***** * of 77.3°; or 1.lm, giving an elevation of 74.6°. Further, even if d is exactly h14, this translates into an elevation of almost exactly 76°, rather than the nominal 75°. In short, even an experienced ladder user may vary 2° or more either side of the recommended attitude. ****

The present invention seeks to limit the variation, as will now be described with particular reference to Figures 3 and 4.

Referring first to Figure 3, this shows a first gauge in the form of a spirit level 20 secured to a ladder stile 14. The spirit level 20 is set parallel with a ladder rung 14 and it is visible from the front by means of a window 22 in the stile 14. Thus the ladder, viewed from the front, can be positioned so that the spirit level 20 gives a horizontal reading, which means the rung 16 is horizontal, and the stile 14 (and therefore the ladder as a whole) is vertical and does not tilt to either side. That is, when the spirit level 20 is at its midpoint or datum position, this signifies that the ladder is vertical as viewed from the front.

io Referring to Figure 4, this shows a second gauge in the form of a spirit level 24 secured to the side of the stile 14. As shown in Figure 4, the spirit level 24 is set at an angle of 75° to the stile 14. Thus, when the spirit level 24 is at its datum, the stile 14 (and therefore the ladder as a whole) is at the recommended 75° angle of elevation.

As so far described, the spirit levels 20 and 24 (which may be replaced by other gauges such as clinometers or tilt meters) facilitate the correct positioning of a ladder before use. However the present invention extends to the monitoring of the ladder during use, as will now be described.

The spirit levels 20 and 24 are contained in a housing 26 (Figure 4) which also contains electrical circuitry for monitoring deviation of each spirit level 20 and 24 away from its datum. The circuitry is not shown in the drawings, for simplicity of illustration, and it is not considered necessary to describe it in detail here. It may include, for instance, two sensors responsive (eg by capacitance variation) respectively to changes in the position of liquid in the spirit levels 20 and 24 and coupled to an alarm that signals when this position changes by more than some permitted amount, the circuit as a whole * .. .** * including a rechargeable battery or other source of power. Returning then to * Figure 4, the housing 26 carries a manually operable switch 28 whereby the *.* * monitoring circuit may be alternatively enabled and disabled, a neon or other light 30 to indicate when the monitoring circuit is enabled and a beeper 32 or , *** the like that provides an audible alarm if the attitude of the ladder goes outside permitted bounds during use. The housing 26 also carries a test button manually operable to test the operation of the beeper 32. Finally with regard to Figure 4, a socket 38 provides means for the battery of the monitoring circuit to be recharged.

The sensors (which may be adjustable) of the monitoring circuit are set so that the beeper 34 is activated if either spirit level 20 or spirit level 24 deviates from its datum by more than 2° in either direction.

Figures 5 to 7 illustrate a form of the invention which can be readily attached to and released from a ladder. In this modified form the housing 26 carries a pair of rubber-coated jaws 40 urged together by a tension spring 42 extending through the housing 26. In use the jaws 40 are spread apart against the tension of the spring 42 to receive and then grip a stile 14 indicated in broken lines in Figure 7. By this means the monitoring apparatus can be attached to a ladder and readily released from it.

Figures 8 and 9 show other means for releasably attaching an attitude-monitoring device to a ladder having a stile 80. The attachment means comprises a box 82 dimensioned to receive the monitoring device.

The box 82 has a closed base, an open top whereby the device is inserted and four inwardly directed wings 84 to hold the device in place in the box 82.

The box 82 has a backing plate 86 having an adhesive rear face whereby it is secured to the side of the stile 80. Tabs 88 on the forward edge of the backing plate 86 provide means whereby the forwards edge of the backing plate 86 is lined up with the front of the stile 80. Then, as can be seen from Figure 9, the box 82 is upright (and a monitoring device in the box 82 is vertical) when the ladder is at the correct angle of 750 The attachment means of Figures 8 and 9 allows an attitude- * monitoring device to be very easily attached to a ladder at the right setting for monitoring its attitude and just as easily removed from the ladder after use for safe storage.

At this point it may be noted that an attitude-monitoring device embodying the invention may be used for purposes other than monitoring the attitude of a ladder. It may, for instance, be used to monitor the attitude of a load on a truck or cargo on a ship. One other use which may have particular benefits is in monitoring the attitude of a person, with an alarm triggered automatically at an assistance station if the person should have a fall. For this purpose, as shown in Figure 10, the monitoring device 90 may be equipped with a loop or bracket 92 whereby the device 90 may be attached to a belt worn by the person to be monitored. In this case the device 90 incorporates a mobile phone arranged to send a call to the assistance station automatically if the device deviates from its normal vertical orientation for more than a short period. (The monitoring device 90 is controlled to exclude transient signals such as those caused by the person's walking or running).

As long as the person remains upright, the monitoring device 90 is quiescent.

If the person has a fall, the assistance station is called automatically. This is of benefit to elderly and/or infirm people, for instance in a nursing home. A similar device can also be of benefit to fit people such as those walking or running or climbing in isolated locations, in which case the monitoring device may also monitor the location of the person (eg by GPS) and signal this to the assistance station. To enable staff at the assistance station to communicate with the person, the mobile phone may be arranged to establish a voice link automatically, and in this case the monitoring device 90 may incorporate a loudspeaker and/or it may be arranged to be worn on a belt or harness at or above chest level.

As an alternative to the pair of spirit levels described with reference to Figures 3 and 4 and with reference to Figures 5 to 7, a monitoring device embodying the invention may -for monitoring the attitude of a ladder or for other purposes such as personal safety -use electronic sensing means. An t.* ..s example of such a device is shown at 60 in Figures 1 1A and 11 B. Device 60 : .. has a housing 62 having closed sides; Figure hA shows a view with the a * front face of housing 62 removed, and Figure 11B shows a view with a side face of housing 62 removed. The device comprises a pendulum 64 attached by a pivot to the housing 62. An LED 63 is mounted in the top of the pendulum. The pivot comprises an axle 65 rotatably attached to the housing and passing through an aperture 66 in pendulum 64, and a centre pin 67 rotatably attached to the pendulum and attached to the first axle. Thus the pendulum can freely rotate around the two horizontal axes. Alternatively, a ball joint or flexible link could be used, or the pendulum could be a flexible whisker and thus not require a pivot. Any freely moving pendulum could be used.

The pendulum 64 contains a magnet 68 embedded in its lower end (shown in dashed lines). The device further comprises an integrated circuit 69. The magnet 68 and the IC 69 form a linear Hall-effect sensor. It is not considered necessary here to discuss the Hall effect, other than to say that in a magnetic field a conductor carrying an electric current gives rise to a transverse voltage that varies with the magnetic field. The voltage output by IC 69 drops when the magnet moves away from it, as occurs when the pendulum swings away from IC 69.

For monitoring deviation from a particular attitude, the pendulum 64 is set up so that its datum position, in which the magnet 68 is positioned above the centre of the IC 69, corresponds to the desired attitude. For a ladder, this is vertical from side to side and at 75° angIe of elevation. Alternatively, the device can monitor deviation from the vertical in both planes and be mounted on the ladder at an angle of 75°, as shown in Figures 8 and 9. If the ladder tilts away from the desired attitude in either the elevational plane or the side-to-side plane, the natural vertical hang of the pendulum 64 causes the magnet 69 to move away from the centre of the IC 69, and this in turns results in a drop in the output voltage. Thus the output voltage provides a measure of the amount by which ladder deviates from its desired attitude.

* *.*** * In a simple form of the device a single sensor is used. Otherwise three : *. sensors may be provided to allow triangulation and hence an exact measure *10 * of the ladder's attitude. In other embodiments other types of sensor may be used that also provide an indication of how far a pendulum has swung away from a datum point.

In one embodiment, the top of housing 62 contains a transparent circular section marked with concentric rings through which LED 63 is visible.

The centre of the rings is directly above the datum position of pendulum 64.

Thus, when lit, LED 63 provides a visual indication of the deviation from the the datum position of pendulum 64. Alternatively, a similar display may be achieved through electronic means, wherein a light is displayed at particular points in a display marked with circular bands. This is described with reference to Figure 13.

As shown by the schematic Figure 12, the device 60 is powered by a supply voltage V. The Hall voltage VH output from the sensor(s) 66 is delivered to a microprocessor 70 by way of an asymmetric filter 72 which compensates for transient signals such as those caused by movement of a user on the ladder or vibration from power tools etc. The microprocessor 70 converts the voltage VH to a number giving a deviation of the pendulum 64 from the datum 68 (Figure 11). The microprocessor 70 drives a visual display 74 (described in more detail hereinafter) that shows the attitude of the ladder against a series of circular bands representing angles of deviation between 0° and 1.50. Alternatively, as shown in Figures 1 1A and 11 B, the operation of LED 63 is controlled elecronically by microprocessor 70 but moves mechanically, controlled by the pendulum.

Above 1.5° degrees an audible alarm 76 goes off. The alarm 76 has four discrete volume levels and is arranged to become louder over time. The device 60 incorporates a push-button switch 78 for cancelling the alarm, which does not cease simply by bringing the angle of deviation back below 1.5°. The device 60 as a whole is turned on and off alternatively by pressing S...

the push-button switch 78 for 3s.

Figure 13 illustrates the operation of monitoring device 60 embodying * .* the invention as attached to a ladder for monitoring the attitude thereof. In Figure 13 different states of operation are identified as Si to S9. Referring in Figure 13 to the first state Si, the monitoring device has on its upper face - * where it can be readily seen by a user -a display indicated at 100 showing S. S S * S S. the attitude of the ladder in elevation, as indicated by arrows X-X, and from side to side, as indicated by arrows Y-Y. (For simplicity of illustration in Figure 13 the detailed references of Si are not replicated for the other operating states S2 to S8).

The display 100 is provided with concentric rings about a central datum representing the correct attitude of the ladder in use. These rings define: a lock zone 102 signifying that the ladder is within 1° of its correct attitude both in elevation and from side to side -ie it is within a range of about 740 to 76° in elevational attitude and within a range of 89° to 910 in side-to-side attitude; a warning band 104 signifying that the ladder is within 2° of its correct attitude both in elevation and from side to side -ie it is within a range of about 73° to 77° in elevational attitude and within a range of 88° to 92° in side-to-side attitude; and an alarm band 106 signifying that the ladder is more than 2° away from its correct attitude in either elevation or from side to side, and is therefore unsafe.

Referring still to operating state Si, the display 100 is provided with light emitting diodes (LEDs) which illuminate to indicate the degree of variation in attitude of the ladder and the direction in which it varies. Again for simplicity of illustration, only one LED 108 is shown in the lock zone 102, one LED 110 in the warning band 104 and one LED 112 in the alarm band 106, although it is to be understood that there may be a plurality of LEDs in at least the warning band 104 and the alarm band 106.

Although not detailed in Figure 13, the monitoring device includes a sounder to provide an audible signal accompanying the visual signal provided by the display 100 and a push button manually operable to activate S...

the device.

In Figure 13, operating state SI is a starting point, before the ladder is * *. to be deployed, Power to the device is off, the sounder is silent and all the LEDs 108 to 112 are out. *.*

To activate the monitoring device, the push button is pressed and released and as indicated by arrow A. This puts the apparatus into operating ** * S. state S2 -characterised as being unlocked in the alarm band. In operating state S2, an LED in the alarm is illuminated (illustrated by a star in Figure 13) at low brightness to indicate that the ladder is well away from its correct attitude. At the same time the sounder signals at low volume and low pitch.

To prepare for use of the ladder, it is next moved closer to its correct attitude as indicated by arrow B. When the ladder is within 2° of its correct attitude, it is in operating state S3 -characterised as unlocked in the warning band -in which an LED in the warning band is illuminated. In operating state S3 the closeness of the ladder to its correct attitude is emphasised by the LED in the intermediately located warning band being brightly illuminated.

The sounder continues to signal at low volume, but now at medium pitch. If the ladder is displaced away from this situation, it reverts to operating state S2, as indicated by arrow C, and then needs to be replaced again.

From operating state S3 the ladder can be adjusted, as indicated by arrow D, into operating state S4, in which the ladder is within 1° of its correct attitude both in elevation and from side to side -ie it is within a range of about 74° to 76° in elevational attitude and within a range of 89° to 91° in side-to-side attitude. In operating state S4, characterised as unlocked in lock zone, the fact that the ladder is now at a safe attitude is signalled by illumination -at a low level -of the LED in the lock zone in the centre of the display 100. The sounder emits a single pip every second, at medium volume and high pitch. If the Jadder is displaced away from this situation, it reverts to operating state S3, as indicated by arrow E, and then needs to be replaced again.

If the ladder remains stable in operating state S4 for 5s, the apparatus *.S.

S..... automatically changes to operating state S5 as indicated by arrow F. In operating state S5, characterised as locked in lock zone and signifying a safe * *. working situation for the ladder, the LED in the central lock zone flashes brightly every second and the sounder is silent.

As long as the ladder remains in operating state S5 it is safe for use. If for any reason it moves out of true by more than 1°, the apparatus changes ** * 0 0* S. as indicated by arrow H to operating state S6, signifying that the ladder is no longer safe for use. In operating state S6, characterised as locked in warning band, the unsafe situation of the ladder is signalled by illumination of an LED in the warning band, which emits a bright double flash every second, and by the sounder emitting a double pip every second at medium volume and high pitch.

If with the apparatus in operating state S6 the user takes corrective action to restore the correct attitude of the ladder, the apparatus returns to operating state S5 as indicated by arrow H. If, alternatively, the user fails to take corrective action and the ladder moves further out of true, then as indicated by arrow J the apparatus goes into operating state S7, signifying that the ladder is now definitely unsafe. Operating state S7, characterised as locked in alarm band, an LED in the outer alarm band of the display 100 pulses brightly and the sounder sounds as a siren in time with the LED pulse at high pitch and with volume increasing progressively to a maximum level.

To cancel the alarm, the user must now press and release the push button of the monitoring device, which as indicated by arrow K puts the apparatus into operating state S2, from which the ladder may be repositioned.

As can also be seen from Figure 13, if the push button is pressed and released in operating state S6 the apparatus goes into operating state S3 as indicated by arrow L, after which it can be repositioned at a new location.

And if the push button is pressed and released in operating state S5 the apparatus goes into operating state S4 as indicated by arrow M, and again the ladder can then be repositioned at a new location.

Also shown in Figure 13 is a starting state S8 in which the ladder is already within 2° of its correct attitude, in which case pressing and releasing * *. the push button as indicated by arrow N will put the apparatus into operating S.. state S3. And if the ladder is in a starting state S9 in which it is already within *.* 1° of its correct attitude, pressing and releasing the push button as indicated by arrow P will put the apparatus straight into operating state S4. * * * S S *.

The monitoring device incorporates three more features as follows.

First, as will be understood from the foregoing description with reference to Figures 8 to 10, a filter eliminates spurious warning or alarm conditions arising from short-period oscillation of the ladder caused by a user ascending or descending or using a power tool etc. Second, if the push button is pressed and held for 5s in any operating state, the monitoring device is deactivated and the ladder can be put away (usually, for security, after the monitoring device has been detached). And third, if the monitoring device is unused for 4hr it is automatically deactivated, and for ongoing use the push button should be pressed and released again.

Various modifications to the apparatus described may be made without departing from the scope of the present invention. For instance, especially for use as a personal safety alarm for walkers and climbers etc the monitoring device may have a Hall effect sensor positioned above the normal level of the magnet, so that the magnet becomes closer to one of the sensois if the person falls (and the device is on its side) and thereby generates a greater output voltage that triggers an alarm. In this arrangement, a plurality of sensors may be provided, in a common normally horizontal plane, so that the alarm is triggered whether the person wearing the device is on his/her back or front or either side. Another form of monitoring device is configured as a tetrahedron having a triangular base with a Hall effect sensor at each corner, If the wearer falls, the magnet drops towards one of the corners, close to one of the sensors, generating an increased Hall voltage to trigger the alarm. Other possible variations and adaptations will be apparent to those skilled in the art. * * *

****** * * * ** ** * *** *

S I.. *.** * I **** ** I * * * * **

Claims

Claims 1. A device for signalling deviation from verticality of a subject, which device comprises an inclinometer operative to measure attitude of the subject in two vertical planes and an alarm connected to the inclinometer to be automatically activated if said attitude in each plane is not within a preset range, characterised in that said device includes switch means manually operable to enable and disable the alarm alternatively.
2. A device for signalling deviation from verticality of a subject as claimed in claim I characterised in that said device includes an indicator operative to show when the alarm is enabled.
3. A device for signalling deviation from verticality of a subject as claimed in claim I or claim 2 characterised in that said device includes test means whereby operation of the alarm may be tested.
4. A device for signalling deviation from verticality of a subject as claimed in any preceding claim characterised in that the inclinometer comprises two spirit levels respectively orientated in said two vertical planes.
5. A device for signalling deviation from verticality of a subject as claimed in any of claims I to 4 characterised in that the inclinometer comprises a pendulum pivoted about two axes respectively orientated in said two vertical planes. * * *

*
6. A device for signalling deviation from verticality of a subject as claimed in claim 5 characterised in that the inclinometer comprises a Hall effect sensor. S...
7. A device for signalling deviation from verticality of a subject as claimed in any preceding claim characterised in that said two planes are mutually orthogonal.
8. A device for signalling deviation from verticality of a subject as claimed in claim 7 characterised in that the switch means is configured and arranged so that its operation requires it to be manually engaged for not less than a predetermined switch period.
9. A device for signalling deviation from verticality of a subject as claimed in claim 8 characterised in that the switch means comprises a push button on the device.
10. A device for signalling deviation from verticality of a subject as claimed in any preceding claim characterised in that the device includes sleep means operative to disable the device automatically if it is left enabled but inactive for a predetermined working period.
11. A device for signalling deviation from verticality of a subject as claimed in any preceding claim characterised in that the device includes smoothing means configured and arranged so that short-period movements of the subject do not activate the alarm.
12. Apparatus for monitoring the attitude of a portable ladder characterised in that said apparatus includes a device as claimed in any preceding claim operative to measure elevational attitude of the ladder in a S..... first of said two vertical planes and side-to-side attitude of the ladder in the second of said two vertical planes. * *4 * * .
13. Apparatus for monitoring the attitude of a portable ladder as S..claimed in claim 12 characterised in that said apparatus comprises a cradle S...for releasable attachment of the device to the ladder, which cradle is * *1 *5 configured and arranged to be secured to the ladder in a setting such that when the device is received in the cradle said preset range includes an elevational attitude of 75° from horizontal in the first plane and a side-to-side attitude of 900 from horizontal in the second plane.
14. Apparatus for monitoring the attitude of a portable ladder as claimed in claim 12 or claim 13 characterised in that the device displays attitude of the ladder against a scale showing said preset range.
15. Apparatus for monitoring the attitude of a portable ladder as claimed in claim 14 characterised in that the scale comprises rings about a datum of the preset range.
16. Apparatus for monitoring the attitude of a portable ladder as claimed in claim 15 characterised in that the rings define a lock zone wherein the attitude of the ladder is within 1 0 from the datum.
17. Apparatus for monitoring the attitude of a portable ladder as claimed in claim 16 characterised in that the rings define a warning band around the lock zone, within which warning band the attitude of the ladder is between 1° and 2° from the datum.
18. Apparatus for monitoring the attitude of a portable ladder as claimed in claim 17 characterised in that the rings define an alarm band around the warning band, within which alarm band the attitude of the ladder S... * .is more than 2° from the datum.

*..*S* * S
19. Apparatus for monitoring the attitude of a portable ladder as claimed in any of claims 15 to 18 characterised in that each ring is provided with means of illumination providing a visual indication of the attitude of the S..ladder relative to the datum. * * S S.
20. Apparatus for monitoring the attitude of a portable ladder as claimed in claim 19 characterised in that the means of illumination is variable in brightness to signal the attitude of the ladder relative to the datum.
21. Apparatus for monitoring the attitude of a portable ladder as claimed in claim 19 or claim 20 characterised in that the means of illumination is configured and arranged to flash to signal the attitude of the ladder relative to the datum.
22. Apparatus for monitoring the attitude of a portable ladder as claimed in any of claims 19 to 21 characterised in that the apparatus includes a sounder providing an audible indication of the attitude of the ladder relative to the datum.
23. Apparatus for monitoring the attitude of a portable ladder as claimed in claim 22 characterised in that the sounder is variable in volume to signal the attitude of the ladder relative to the datum.
24. Apparatus for monitoring the attitude of a portable ladder as claimed in claim 22 or claim 23 characterised in that the sounder is configured and arranged to pulse to signal the attitude of the ladder relative to the datum.
25. Apparatus for monitoring the attitude of a person characterised in that said apparatus includes a device as claimed in any of claims I to 11 * ** *** * and a carrier whereby the device may be carried by the person to monitor that the person is upright, wherein said alarm is automatically activated if the person carrying the device ceases to be upright for more than a monitoring period. * S S... * S * S S *S
26. Apparatus for monitoring the attitude of a person as claimed in claim 25 characterised in that said apparatus includes a transmitter operative automatically to transmit from the device a signal representative of the activated alarm.
27. Apparatus for monitoring the attitude of a person as claimed in claim 26 characterised in that said transmitter includes a mobile telephone programmed to send an outgoing call automatically when the alarm is activated.
28. Apparatus for monitoring the attitude of a person as claimed in claim 26 or claim 27 characterised in that the mobile telephone is configured and arranged so that the person carrying the device may establish voice communication by way of said call.
29. Apparatus for monitoring the attitude of a person as claimed in any of claims 25 to 28 characterised in that said apparatus includes means monitoring the location of the device and the transmitter is operative to include information identifying said location in said signal. * S ***.S*SSSSS * S * 55 * S S 5*5 S * **S **S. * S 555. 5.S S * S.