GB2276969A - Alarm system - Google Patents

Abstract

The alarm system is for use primarily, though not exclusively with infant carriages, and comprises a pressure sensitive pad (SW5), a motion detector (SW1, SW2), and a personal alarm trigger mechanism (8), all of which are operatively connected to an alarm (4) via a control unit in such a manner that the system has a number of distinct modes of operation including personal protection mode whereby the alarm is set off by use of the personal alarm trigger mechanism and carriage protection mode whereby the alarm is set off only in the event that either pressure is released from the pressure sensitive pad or the motion detector is activated. <IMAGE>

Description

ALARN SYSTEM The present invention relates to an alarm system particularly, though not exclusively, used to protect a carriage such as a pram/buggy and/or a child carried therein.

If a child is left in an unattended carriage even for a short time, there is a real risk that the child may be snatched from the carriage, or the carriage stolen. It is therefore convenient to mount on the carriage an alarm system that would indicate by audible or other means that such an event had occurred.

Such devices have been proposed, for example that described in the Applicant's own British Patent Number 2163885 which describes a system comprising a pressure sensitive pad, removal of pressure from which triggers an audible alarm. The carriage itself is protected by means of a lead which is placed for example around an immovable object such that the lead will be broken thus triggering the alarm if an attempt is made to push the carriage away.

Whilst this type of system goes some way to solving the problem referred to above, there remains the need, so far unfulfilled, of an enhanced alarm system which would be more convenient to use and would also give additional protection in the event of an attack on either the child in the carriage or the parent or guardian pushing the carriage.

According to the present invention there is provided an alarm system comprising a pressure sensitive pad, a motion detector, and a personal alarm trigger mechanism, all of which are operatively connected to an alarm via a control unit in such a manner that the system has a number of distinct modes of operation including personal protection mode whereby the alarm is set off by use of the personal alarm trigger mechanism and carriage protection mode whereby the alarm is set off only in the event that either pressure is released from the pressure sensitive pad or the motion detector is activated.

Whilst the second of the two modes referred to immediately above is referred to as "carriage protection", this term is intended, when the system is used for protection of a child in the carriage, to cover protection of both the carriage and the child contained therein.

Conveniently, there is also a third mode in which the whole alarm system is completely deactivated.

Preferably, the personal alarm trigger is in the form of a lanyard which is inserted into a socket switch on the alarm system, the lanyard then being worn by the parent or guardian.

To set off the alarm when the system is in personal protection mode, the lanyard is simply pulled out of its socket. The alarm, which typically comprises a 110 decibel siren, would then sound and continue to do so until such time as the lanyard was replaced in the socket.

Preferably, the motion detector comprises at least one mercury filled switch comprising an arcuate channel and a mercury bead within the channel such that movement of the bead within the channel beyond a certain threshold activates the detector and sets off the alarm.

The threshold referred to above is preferably a time threshold such that the detector is only activated if "continuous" motion for a predetermined length of time (typically a few milliseconds) is detected. This enables the system to "ignore" slight movements such as rocking the carriage - only substantial and continued forward or backward motion would activate the alarm.

Preferably, the motion detector comprises a number of separate switches, for example a main switch and two additional switches all connected together in series.

Whilst mercury switches are preferred, other types of motion detectors could be utilised with equal effect.

Conveniently, the system includes a time out facility such that the alarm, once activated, will sound for 20 seconds and then switch off. However, in the event that the buggy is still moving after this time, the alarm would immediately reactivate.

Preferably, the system is operated by means of a three position key switch, having left, central and right positions corresponding to personal protection, complete deactivation and carriage protection respectively.

A key is inserted into the key switch, the key then being used to switch the system between modes as will be described more fully hereinafter.

Conveniently, the alarm system is included in a weatherproof case with fixing means enabling it to be attached to part of the carriage, for example the upper part of the handle(s).

An embodiment of the present invention will now be described, by way of example, with reference to the accompanying drawings, in which: Figure 1 is a circuit diagram showing the various components of the system, and Figure 2 is a plan view of the system showing the physical appearance of the components on the printed circuit board, Figure 3 illustrates the system attached to the handle of a child's buggy, and Figure 4 illustrates a mercury switch, being one example of a motion detector suitable for use with the system of the present invention.

Referring to the drawings, an alarm system 10 according to the present invention is powered by a battery 2 and comprises a three position switch SW3, a personal alarm switch socket SW4, a pressure mat switch SW5 and two motion detectors SW1 and SW2 (SW1 to detect motion and SW2 to detect rocking), all of which are connected as illustrated, via a network of capacitors, diodes, resistors and NOR logic gates to a siren 4.

The system is incorporated within a weatherproof case 24 which has fixing means 24a, 24b to enable the case to be secured to for example a handle 26 of a child's buggy.

The circuit includes a number of logic gates which have been notionally divided into four functional blocks 12,14,16 and 18.

Block 12 comprises two NOR gates 12a and 12b. One of the inputs of 12a is connected to switch SW1 (the main motion detector) and one of the inputs of 12b is connected to SW2 (the motion detector designed to detect rocking or other slight movements). The output of 12b forms the other input of the other NOR gate 12a. Gate 12a is enabled by turning the key to key switch position SW3R. This functional block 12 operates as follows. The gates 12a and 12b form a short time monostable with a period of approximately 2 seconds. SW1, the motion detector, is connected to trigger this operation and SW2 to reset it. The output from the monostable is integrated by resistor R5 and capacitor C9 therefore forming a short time delay before triggering the main alarm.

Switches SW1 and SW2 may comprise mercury switches such as that illustrated in Figure 4. This is essentially an arcuate channel 30 having a series of pairs of electrical contacts 32 and a mercury bead 33. Motion is detected when the mercury bead moves along the channel and makes contact between adjacent contacts. Such a switch may be operated in such a manner that it will only be triggered if a particular contact or series of contacts in a predetermined sequence is made by the mercury bead, so that this facility can be utilised in the present invention to ignore slight movements such as rocking etc.

However, it should be appreciated that the present invention is not limited to the use of a mercury switch, and other types of motion detectors are within its scope.

Functional block 14 comprises two NOR gates 14a and 14b with one of the inputs of 14a being connected to both the pressure mat switch SW5 and the output of gate 12b. This functional block 14 is a monostable with a time period of approximately 40 seconds. This is triggered by the pressure mat SW5 and the output from the integrator R5,C9 connected to functional block 12. The output from block 14 is used to turn on and off the siren formed by blocks 16 and 18. Block 14 also has a power on re-set generated by capacitor 14c and resistor RX6 to ensure that when the unit is first turned on it is in a stable condition.

Functional block 16 comprises two series-connected NOR gates 16a and 16b, the two inputs of 16b being connected together and to the output of 16a. One of the inputs of 16a is connected to the personal alarm (lanyard) switch SW4. Gate 16a is enabled by turning the key to key switch position SW3L. This functional block 16 forms a tunable oscillator which is frequency modulated by the output from functional block 18 and drives the output sounder formed around 4, via transistor 20.

The siren 4 is switched on and off by a transistor 20, the base of which is fed by functional block 16 as explained above.

Functional block 18 comprises two series-connected NOR gates 18a and 18b, the two inputs of 18b being joined together and to the output of 18a. One of the inputs of 18a is connected to the collector of transistor 22. This functional block 18 is a fixed frequency oscillator with a frequency of approximately 2Hz. The output of this is used to frequency modulate block 16 via resistor R8 and diode D4, thus forming a two-tone sounder output.

The operation of the system will now be described with reference to its use to protect a buggy carrying a child.

When pushing the buggy, the parent inserts a key 6 into switch SW3 and turns the switch to the left (SW3L) to put the system into personal protection mode. A lanyard 8 is inserted into socket switch SW4, the lanyard then being worn by the parent whilst pushing the buggy. In the event of an attack taking place on either the parent or the child, the lanyard is simply pulled out of the socket SW4 to activate the siren 4, which would deter any would-be attacker, including animals.

Should the parent wish to stop the buggy temporarily whilst attending to the child, the key is turned to the central position (SW3c) to completely deactivate the system.

When the buggy is to be parked, the key switch SW3 is placed into the right hand position SW3R (corresponding to carriage protection mode which operates in two ways) and the lanyard is removed from the socket switch SW4. Upon parking the buggy the child is protected against removal from the buggy by the pressure sensitive pad connected to SW5, the pad being placed under the mattress in the buggy. Should the child be removed, the alarm is activated by the pressure being released from the pad, thus opening switch SW5. Additionally, should an unauthorised attempt be made to remove the buggy the motion sensor SW1 will immediately activate the siren which then continues to sound for 20 seconds before switching off, reactivating after this time if the buggy is still moving.

Claims (11)

1. An alarm system comprising a pressure sensitive pad, a motion detector, and a personal alarm trigger mechanism, all of which are operatively connected to an alarm via a control unit in such a manner that the system has a number of distinct modes of operation including personal protection mode whereby the alarm is set off by use of the personal alarm trigger mechanism and carriage protection mode whereby the alarm is set off only in the event that either pressure is released from the pressure sensitive pad or the motion detector is activated.

2. An alarm system according to Claim 1 wherein there is also a third mode in which the whole alarm system is completely deactivated.

3. An alarm system according to Claim 1 or Claim 2 wherein the personal alarm trigger is in the form of a lanyard which is inserted into a socket switch on the alarm system, the alarm being set off (when the system is in personal protection mode) by pulling the lanyard out of its socket.

4. An alarm system according to any of the preceding Claims wherein the motion detector comprises at least one mercury filled switch comprising an arcuate channel and a mercury bead within the channel such that movement of the bead within the channel beyond a certain threshold activates the detector and sets off the alarm.

5. An alarm system according to Claim 4 wherein the threshold is preferably a time threshold such that the detector is only activated if "continuous" motion for a predetermined length of time is detected.

6. An alarm system according to any of the preceding Claims wherein the motion detector comprises a number of separate switches, for example a main switch and two additional switches all connected together in series.

7. An alarm system according to any of the preceding Claims wherein the system includes a time out facility such that the alarm, once activated, will sound for a predetermined time and then switch off.

8. An alarm system according to Claim 7 wherein should motion still be detected by the motion detector at the end of the predetermined time, the alarm would immediately re-activate.

9. An alarm system according to any of the preceding Claims wherein the system is operated by means of a three position key switch, having left, central and right positions corresponding to personal protection, complete deactivation and carriage protection respectively.

10. An alarm system according to any of the preceding Claims wherein the system is included in a weatherproof case with fixing means enabling it to be attached to part of a carriage, for example the upper part of the handle(s) of said carriage.

11. An alarm system substantially as herein described with reference to and as illustrated in the accompanying drawings.