GB2060965A - Portable alarm system - Google Patents

Abstract

An alarm device for use by an elderly or infirm person includes an alarm transmitter (1) which is switched on by a wearer-operated push-button (5) to emit an alarm signal. This alarm signal is modulated, e.g. by a 1 KHz signal from an alarm modulator (3). This signal is responded to by a radio receiver (10), whose output is fed to an alarm trigger (13) via a switchable filter (11). To ensure that a fault in the alarm device, e.g. a flat battery, is detected, the alarm device has a further modulator (4), which is clock-controlled to emit a signal with a different modulation to that used for the alarm at preset intervals. At the receiver, these pulses are passed via a filter (12) to a delay timer (14), which operates a fault indicator when a preset number, e.g. two, of pulses have failed to arrive. This gives an indication, either to a warden or to the user, as a result of which the fault can be corrected. The circuitry to drive the timer (14) is also used to drive a clock display. <IMAGE>

Description

SPECIFICATION Portable alarm system This invention relates to a portable alarm device, for use, inter alia, by elderly and/or infirm people.

Elderly people living alone in private accommodation sometimes need to call outside assistance in time of emergency. Of the variety of means available for this purpose, a typical system uses a compact transmitter carried by the person and having an alarm push-button, coupled to a receiver within the household, which serves to relay the alarm to the outside world, either by landline connection to a warden or other authority, or by automatically dialling a preset telephone number or sequence of telephone numbers. A disadvantage of such a system is that the failure of the transmitter battery, or the development of some other fault, disables the system without warning.

According to the present invention there is provided a portable alarm device, which includes a transmitter for sending signals of the type which do not use a physical conductor connecting the transmitten to an associated receiver, a control switch for said transmitter which when operated by a user causes the transmitter to emit a signal of a first type, which signal serves as an alarm signal, a timing device powered from the same power supply as the transmitter and adapted to generate timing signals at preset intervals, and means responsive to each of said timing signals to cause the transmitter to emit a signal of a second type, the fact that the transmitter emits the signals of said second type at said preset intervals indicating that the alarm device isfunc- tioning.

An element of consumer resistance lies in the possible reluctance of some elderly people to admit that they need an emergency alarm system. This can be overcome by providing that the alarm transmitter has a secondary, but ostensible, function of an entirely conventional nature, such as a timepiece.

Hence, commercial advantages exist in exist in exploiting a combined unit, styled as a fob watch or wristwatch and including an alarm device.

In the following description it will be shown that there can be a close compatibility in the technical solutions to the two above requirements, making possible an economical and compact unit.

An embodiment of the invention will now be described with reference to the accompanying drawing. Alarm systems such as described herein, having a person-carried transmitter and a local receiver, might use one of several transmission media. Sonic, ultrasonic, magnetic low and high frequency radio, and even optical propagation have all been suggested. However, although the present arrangement could use any of these, the arrangement described herein uses a radio link, as this is likelyto emerge as the preferred medium. There is the added consideration that the timepiece unit, and the manner in which it is handled and worn, favours the design of a radio antenna and leaves radio propagation as the medium least likely to be obscured in use.

In its simplest form, the person-carried transmitter remains inactive until the alarm button is pressed, whereupon the transmitter radiates for a period sufficient to activate the receiver and initiate the alarm sequence. In a radio system, the simple unmoduiated carrier, on a predetermined frequency, could be sufficient, or tone or pulse modulation might be added to improve discrimination against other signals. In the present case we assume that the alarm transmission is an RF carrier modulated with a single continuous tone. Typical carrier frequencies might be around 150 MHz or even as low as 100 KHz or less, with a convenient modulation frequency being 1 KHz.

To ensure that the system cannot fail un-noticed, as a result of transmitter battery failure or some other fault, the transmitter is arranged to transmit a supervisory signal at regular intervals while the system is operational. This signal might be another modulating tone having a frequency conveniently removed from the alarm frequency, in this case 400 Hz. Hence, underthe control of an internal timing circuit, the transmitter emits a spaced succession of single pulses of carrier plus 400 Hz modulation. The pulse is long enough to be detected reliably by the local receiver, can have a duration of one second.

The pulse repetition rate is once a minute, or it might by as infrequently as once a day, depending upon other operational parameters.

Thus in the drawing we see the transmitter 1 with its own antenna 2, controlled by two modulators 3 and 4. The modulator 3, when enabled by the operation of an alarm push-button 5, generates a 1 KHz signal which is applied to the transmitter 1. The push-button operation also enables the transmitter so that the alarm signal is transmitted.

The other modulator 4 generates a 400 Hz signal which when generated is applied to the transmitter 1 for transmission thereform. This is controlled by clock circuits 6 which are driven from a wrist watch arrangement 7 when the alarm device is combined with an electronic wrist watch or fob watch. The clock circuits 6 generate control pulses at the desired rate, e.g. one per minute as mentioned above, and each of these pulses is applied to the modulator 4 and to the transmitter 1. Hence the latter is caused to regularly emit pulses for supervision.

If a fault occurs, and the supervision signal ceases to be emitted, the elderly person (unless deceased) when realising that the fault has occurred rectifies it (e.g. by changing the battery), and then depresses the reset button 8, which causes the supervisory pulses to be resumed.

The local receiver 10 tuned to the transmitter carrier frequency, has a demodulator feeding two narrow-band filters 11 and 12 tuned respectivelyto 1 KHz and 400 Hz, (or to two such other frequencies as chosen). The normal alarm function, in which pressure of the alarm button initiates carrier plus 1 KHz modulation, gives an output from the 1 KHz filter 11 only, which triggers the normal alarm sequence via alarm trigger 13. Independently, and without prejudice to the normal alarm function, the 400 Hz filter 12 is producing an output in response to each supervisory pulse. This output is made to inhibit a local alarm and lamp indicator which would other wise signal system failure. This is done via a fault delay timer 14, which delays response to avoid transient faults causing trouble.When the timer 14 accepts a fault it lights a fault lamp 15. Assuming that the supervisory pulse interval is once a minute, the time-constart of the 'system failed' indicator mechanism might be made two minutes, under control of clock circuits 16, so that the failed condition would not be indicated until two successive supervisory pulses had been missed.

Since the 'system failed' indication must inevitably be given unless the circuit receives a pulse from the 400 Hz filter within two minutes, the whole system is protected from the transmitter battery through the RF link and up to the 400 Hz filter output.

By making the 'system failed' indicator a gravity or spring operated mechanical flag, this protection might be extended to cover failure of the mains supply to the complete receiver unit, including the failure indicator.

The 'system failed' indicator as described would be intended to give local indication to the elderly person, who might respond by changing the transmitter battery or making personal contect with the appropriate service agency. However, it would also be possible to route the 'system failed' signal as a non-urgent message to the warden or normal recipient of the alarm signal.

Although the system has been described with certain operating times and frequencies, clearly a variety of other values might be adopted. Other variants might include the substitution of a digital pulse code group for the 1 KHz 'alarm' modulation, and a different pulse code group for the 400 Hz 'failure alarm suppression' signal. This would enable the audio-frequency filters to be replaced by the integrated digital decoding circuits, giving greater immunity to interfering signals and having other possible design advantages. Another variant would be for the transmitter to emit two different unmod- ulated carriers, one as an alarm signal and one as a fault signal. Further this self-monitoring system can equally-well be applied to systems exploiting acoustic (ultrasonic), magnetic, optical or other propagating media.

Although the spacing of the 'failure alarm suppression' pulses might be determined by a simple RC time constant, it would be desirable, in the interest of transmitter battery economy, to transmit these pulses as infrequently as the operational circumstances permit. Hence, if the pulse separation can exceed, say, once per minute it would be preferable to determine this by a clock mechanism.

This is achievable by the use of an integrated circuit digital wristwatch chip, now freely available at low cost. A similar chip might be used to determine the time constant of the failure alarm circuit, making it possible to adjust the system to respond very promptly to a missed supervisory pulse.

With the essential clock mechanism already present in the transmitter unit, the hours and minutes display panel is retained as an additional facility for the wearer. Furthermore, the usual option of a day and date display can permit programming the system to ignore periods when the user is regularly absent from home.

The design and operating procedure for the system described above might be summarised as follows. The alarm transmitter is styled externally as a wrist of fob watch, and its normal time-indicating function enables it to be worn openly by the elderly person without embarrassment. An additional push button is provided to enable the alarm to be given when needed. The transmitting antenna can readily be incorporated into the wrist or neck band. The timing circuits automatically activate the transmitter for a brief 'failure alarm suppression' pulse at regular intervals throughout the working life of the system. In the interest of battery economy, these pulses might be limited to only a few milliseconds in duration and a repetition rate of once an hour.

The local receiver is installed in the room most usually occupied by the user, but has a range of, say, 25 metres to permit movement, e.g. into a garden. Its response to the signal resulting from pressure of the alarm button is either two transmit an alarm signal by landline to a local warden or to initiate the calling of one or a sequence of telephone numbers by an automatic dialler. The receiver has an electronic timing mechanism set to activate a local lamp and/or audible alarm, indicating system failure, within a short period of failing to receive a 'failure alarm suppression' pulse. The provision of an external time display on the receiver enables it to double as a mantel clock - a further attack on customer resistance. Synchronism of the fault alarm mechanism is thus readily achieved by ensuring that both clocks show the right time.

Brief departure by the wearer beyond the range of the system could result in a missed suppression pulse and hence a fault indication, but, since this indication is normally only local to the user, a simple test and reset procedure clarifies the true position. A reliable method for achieving this is to provide a further button on the transmitter by which the suppression pulse might be transmitted at any time.

Typically, the user might return from a shopping expedition to find the 'fault' lamp alight. A touch on the suppression button on the wristwatch transmittes would extinguish the lamp and give assurance that the system was still working. For further assur- ance, provision might also be made for displaying, locally, the result of pressing the 'alarm' button, the external alarm circuits being temporariiy disabled, although any such 'test' mode should restore itself to normal after a short period, without deliberate action by the user.

Claims (8)

1. A portable alarm device, which includes a transmitter for sending signals of the type which do not use a physical conductor connecting the transmitterto an associated receiver, a control switch for said transmitter which when operated by a user causes the transmitter to emit a signal of a first type, which signal serves as an alarm signal, a timing device powered from the same power supply as the transmitter and adapted to generate timing signals at preset intervals, and means responsive to each of said timing signals to cause the transmitter to emit a signal of a second type, the fact that the transmitter emits the signals of said second type at said preset intervals indicating that the alarm device is functioning.

2. A portable alarm device which includes a radio transmitter for sending signals to an associated radio receiver, a control switch for said transmitter which when operated causes the transmitter to emit a radio signal of a first type, which signal serves as an alarm signal, a timing device powered from the same power supply as the transmitter and adapted to generate timing signals at preset intervals, and means responsive to each of said timing signals to cause the transmitter to emit a signal of a second type, the fact that the transmitter emits signals of the second type at said preset intervals indicating that the alarm device is functioning.

3. A device as claimed in claim 2, and in which the the signals of said two types are the transmitter's carrier frequency modulated by different audio frequencies.

4. A device as claimed in claim 2, and in which the signals of said two types are two different carrier frequencies from the transmitter.

5. A device as claimed in claim 2, and in which the signals of said two types are the transmitter's carrier frequency conveying two different code groups.

6. A device as claimed in any one of the preceding claims, and in which the timing device also drives a visible clock display.

7. A portable alarm device substantially as described with reference to the accompanying drawings.

8. An alarm system as claimed in any one of claims 1 to 7, and in which the receiver means also includes timing means which controls a clock.