For many years it has been customary practice to provide security alarm systems for places such as banks and wages offices where large sums of money and other valuables are to be found. There is also a growing need for security alarm systems for use against intruders at entries, such as front doors, for domestic premises as .well as such place. Often such security alarms systems for such places have taken the form of an alarm which can be set off by a bell push or other actuating means in response to a.threat from an intruder. Such systems, however, are not altogether satisfactory as the intruder may prevent actuation of the alarm or may respond violently to an attempt to actuate the alarm. It is thus an object of the present invention to provide a security alarm system of the type which are operative to provide an alarm signal when an employee fails to carry out a cancelling or deactivating operation. Also there is well-recognised danger that invalids

or infirm persons living along will suffer further in¬ capacity without having sufficient time to make their need for assistance known. Various devices have been proposed to assist such persons in make their incapacity known but the majority of these devices presently available commercially rely upon the person operating some form of warning device, for example, placing a card in the window of their dwelling or pressing a control to actuate a mechanical or electrical warning device. It is a further object of this invention to provide an improved alarm system for invalids or infirm persons of the type which are operative to provide an alarm signal when the person fails to carry out a cancelling or deactivating operation. „ According to the present invention, there is provided an alarm system comprising a primary timer for providing a first alarm signal at a predetermined first time interval; preliminary alarm means actuated by said first alarm signal to indicate that said first interval has expired; a secondary timer for providing a second alarm signal at a predetermined second time interval afte actuation of the preliminary alarm means; main alarm means actuated by said second alarm signal to indicate that the combined first and second time intervals have expired; and a manually operable override control operabl at any time during said first and second time intervals

- 3 - to cancel said f irst alarm signal or sa id second alarm signal .

In one embodiment the invention provides an entry security alarm, the alarm system being activated before 05 an entry, e.g. front door, is opened to a stranger, the override control deactivating the alarm system as well as cancelling the first or second alarm signals.

In preferred embodiments of the invention the primary timer -provides the first alarm signal at 10 consecutive predetermined first time intervals, the over¬ ride control being operable during each of said con¬ secutive first time intervals and corresponding second time intervals to cancel the first or second alarm signals. Thus the alarm system may be specifically 15 .activated, e.g. during a period of high security risk, or may be continuously activated, for instance as an alarm for invalids or infirm persons living alone; providing continuing consecutive first time intervals and first and second alarm signals which must be 20 cancelled periodically to prevent actuation of the main alarm means.

Preferably, the alarm system is electrically powered, by, for example, mains voltage or accumulators such as dry cell batteries. Thus, the timer can be an 25 electric clock and the alarm means can be an electrically illuminated sign. The use of accumulators renders the

system of the invention independent of the mains electricity supply to the place or dwelling in which it is used. It is preferred that the system should include rechargeable accumulator(s) and a mains voltage 05 charging circuit whereby the system is normally powered by mains voltage but will operate on the accumulator(s) in the event of a mains voltage failure.

In a particularly preferred embodiment the primary timer comprises a binary divider to which period¬ ic ic electrical impulses are applied. Suitably, the primary and secondary timers are in an electrical citcuit comprising CMOS-type integrated circuits, especially binary ripple counter(s) and AND gate(s). The primary and secondary timers may be incorporated in a single 15 .timer.

The primary timer can be adapted to provide an alarm signal at consecutive predetermined first time intervals, the duration of which intervals are inde¬ pendent of operation of the override control. Alter- 20 natively, said time intervals can commence with each occasion that said control is operated and be prematurely terminated upon next operation of the override control within the predetermined time interval. The predeter¬ mined first and second time intervals can be fixed when 25 assembling the timer or provision can be made for ad¬ justing said intervals as required. Equal predetermined

first time intervals can be provided or the timer pro¬ grammed to provide predetermined major time intervals of different lengths depending upon the time of day. For instance, two or three hour intervals can be provided during normal waking hours, e.g. 9 a.m. to 10 p.m., but a single, e.g. eleven, hour interval provided overnight.

The preliminary and main alarm means can be audio and/or visual alarms but preferably the main alarm means is visual with or without a supplementary audio alarm. Usually, the main alarm will be located at a pos¬ ition remote from the timer. It is especially preferred that said main visual alarm should be an illuminatable sign adapted to be continuously or intermittently (i.e. flashing) illuminated in response to the alarm signal. Advantageously, the sign is adapted to be displayed in a window by, for example, standing on a window sill or secured to the window glass. Suitably the sign includes words or a device which when illuminated clearly indi- cates to a passer-by that assistance is required. For example, the sign might have the letters "S.O.S." or the word "HELP".

The override control is manually operable and can be located remote from or adjacent to the primary timer. Suitably said control can be a press-button which when depressed closes an electrical circuit to cancel the next

preliminary alarm signal. Alternatively, said press- button can operate a. echanical linkage to serve the same purpose. It is important to note however that in alarm systems in which the primary timer provides the first alarm signal at consecutive predetermined time intervals the override control is adapted to cancel only the next preliminary alarm signal due and not subsequent preliminary alarm signals and that such cancellation can be effected at any time during the respective first time interval. In this manner, the alarm system of this invention is quite distinct from conventional clock alarms in which any override control cannot be operated once during each sequential time interval to cancel only the next alarm signal. Conventional alarm systems require L separate operation to release the override control after the due time for an alarm signal in order to act¬ uate the alarm for the next signal due.

It will be appreciated that the preliminary timer provides an alerting signal a short time before the main alarm means operates in .order to remind the user that the override control has not been operated within the major time interval. In this manner inadvertant oper¬ ation of the main alarm means can be avoided.

It will be appreciated that the alarm system of this invention will provide an indication of the expiry of any predetermined time interval during which the over-

- 7 - ride control is not operated. Thus incapacity of the user to the extent of not being able to operate the override control will be indicated after expiry of said interval. Conveniently, the alarm system can be accommodated within a single housing of, for example, plastics mat¬ erial, although it is possible for the components parts thereof to be located in different positions in the dwelling. The alarm system can incorporate a temperature- sensitive override control to automatically actuate the main alarm means in the event that the temperature at a monitored location falls below and/or rises above pre¬ determined threshold value(s) . Thus the system can -provide a warning of a risk of hypothermia and/or a fire alarm. Moreover, the system usually will have a manually operable switch to immediately actuate the main alarm in the event that immediate assistance is required.

The following is a description by way of example only and with reference to the accompanying drawings of alarm systems in accordance with preferred embodiments of the present invention. In the drawings:-

Figure 1 is a block diagram of an alarr ^* * system in accordance with a first preferred embodiment of the invention, and

Figure 2 is a circuit diagram of an alarm system

in accordance with a second preferred but simplified embodiment of the invention.

Referring first to Figure 1 , an alarm system comprises an electrical charger 1 supplied with mains voltage electricity and charging a bank of rechargeable accumulators 2. A primary timer 3 is powered by said accumulators 2 and is arranged to provide a preliminary alarm signal after a predetermined major time interval of, for example, 24 hours. Said signal actuates a secondary timer 4 but manual operation of a cancel/reset switch 5 at any time resets the primary timer 3 to commencement of the time interval and cancels both said alarm signal and an alarm signal from the secondary timer if said signal(s) have been generated. The sec- pndary timer 4 provides a main alarm signal after a predetermined minor time interval of, for example, 5 minutes, following actuation unless the switch 5 is operated in the interim.

The preliminary alarm signal actuates a preliminary alarm 6 which can be a buzzer and/or lamp and which is intended to be located within a dwelling in which the system is to be installed. Accordingly, alarm 6 con¬ stitutes, a reminder to the user of the system to operate the switch 5 unless a main alarm 7 is to be given. The alarm 7 can be a buzzer and/or lamp and is intended to be located remotely from the switch 5, usually externally

of the dwelling, to attract the attention of persons other than the user of the system.

A manually-operable emergency switch 8 is con¬ nected in parallel with the timers 3, 4 to override said timers and provide immediate actuation of alarm 7 if urgent assistance is required.

A low temperature sensor 10 is connected in parallel with timer 3 to provide the preliminary alarm signal in the event that the temperature of the mon- itored location falls below a predetermined minimum level. Similarly, a high temperature sensor (i.e. fire sensor) 9 is.connected in parallel with switch 8 to provide the main alarm signal in the event that the temperature at said location exceeds a predetermined jnaximum level.

Usually, the major and minor time intervals will be fixed during manufacture but adjustable timers 3, 4 can be provided if required.

The components 1 to 6 and 8 to 10 conveniently are located in a single housing with the main alarm 7 remote therefrom.

The timers 3, 4, switches 5, 8 and alarms 6, 7 can be incorporated in a circuit substantially as shown in Figure 2, which figure shows a circuit corresponding to a block diagram differing from Figure 1 in that items 1 , 2, 9 & 10 are omitted.

Referring to Figure 2, a 240 volt A.C. mains electrical supply 5 is applied to the primary winding of a transformer 11 having two 12 volt secondary windings. The voltage VCC derived from one of said secondary windings is applied to the respective last pins of integrated circuits A, B, C, D constituting the primary and secondary timers 3, 4. The voltag.e VDD derived from the other of said secondary windings is applied to the alarms 6, 7 as shown. The integrated circuits are of the CMOS-type with A and B being

14 stage binary ripple counters (reference CD 4020) and C and D being quad 2-input AND gates (reference CD 4081) . The circuit diagram employs standard graphical symbols and does not require detailed explanation except .n respect of the alarms 6, 7. Alarm 6 comprises a green lamp δa_ in parallel with a buzzer 6b whereas alarm 7 comprises an illuminatable "HELP" sign 7a_, a loud buzzer 7b_ and a red lamp 7c. The lamp lc is mounted adjacent lamp β_b on a housing enclosing the circuit except for sign 7a_ and buzzer 7b which are intended to be located remotely from the housing, for example externally of a dwelling in which the alarm is situated or in a window of said dwelling.

It will be appreciated that the invention is not restricted to the details described above with reference to the drawings but that numerous modifications and

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- 11 - variations can be made without departing from the scope of the invention, as defined in the following Claims. It will be appreciated also that the alarm system is of use for purposes other than as an alarm to bring assis- 05 tance to elderly or infirm persons. For example, the system could be readily adapted for security use whereby an alarm is given if a guard fails to operate the over¬ ride control within the relevant time period.

In a particular variation of the alarm system 10 described with reference to Figure 1, the electrical charger 1, rechargeable accumulators 2, the manually- operable emergency switch 8, the high temperature sensor 9 and low temperature sensor 10 components are omitted from the system. Additionally the primary timer 3 is 15 .provided with an activator switch (not shown) and the cancel/reset switch 5 is not adapted to reset the primary timer 3 but only cancel the first and second alarm signals. This variation of the system is particul¬ arly suitable as an entry alarm system, being activated 20 by the activator before an unknown person is allowed to enter, e.g. on opening of 9 a domestic front door. If the unknown person turns out to be an unwanted intruder, the cancel/reset switch is not used resulting in the setting off of the external alarm 7.