Security alert apparatus

Abstract

 Security alert apparatus comprises a receiver unit 11, and one or more transmitter units. Each transmitter unit is programmed to emit signals in 20-30 msec bursts at 3-4 second intervals, the signals being 20-bit or greater randomly generated pseudo-unique identification codes. The receiver unit is initialised to learn the codes, and then compares codes contained in signal bursts with learned and stored codes.
If any learned code is not detected within a prescribed period (greater than the burst repeat interval) an alarm is generated. The transmitter units may be fixed to articles of property or to children to guard against mislaying, theft, straying, or abduction.

Description

[0001] This invention relates to a security alert apparatus, in particular to such an apparatus adapted to give warning if a target has moved outside a predetermined range.

[0002] The invention is intended to provide monitoring of one or more valuable items, or persons, for example to warn of theft or mislaying of personal items such as hand luggage, or straying or abduction of people, such as children from the proximity of their carer.

[0003] US Patent 4,462,022 (Stolarczyk) describes a security apparatus comprising a central control unit which is in radio-frequency communication with one or more transmitters each associated with a remote sensor, for security monitoring. The transmitters are each operated at intervals of the order of thirty seconds, for a period of about one second and each transmitter emits a signal modulated with an identifying code for the respective transmitter. The system is envisaged for monitoring eg intruder, fire detection and other fixed sensors in a fixed site such as a building. The selected codes are keyed manually into the transmitter units, and to the control unit for sensor identification. Such manual coding entails the risk of operator error due to defective memory, or mis-keying to produce duplicated or non-matching codes.

[0004] US Patent 5714932 (Castellon) describes a security apparatus which comprises a central control unit and a plurality of remote transmitters fitted to tags, such as wrist tags for children who are free to move about a site such as a camp site or school campus. Each transmitter has its own narrow band frequency within a wide band monitored by the central unit. The central unit includes a threshold detection circuit which determines when a signal from a transmitter is too faint, and includes a direction finding capability by means of multiple receiver antennae which makes the control unit complex. The transmitters each have a code signal which is interrupted if the tag becomes detached, but continues to emit a carrier wave. The codes are manually input to the transmitters and the control unit, which again provides an occasion for operator error through mis-typing or defective memory so that duplicated or non-matching codes may be entered. The apparatus also includes a hand held detector which can be used for tracking detached tags, or straying children for example.

[0005] Neither of the above systems is satisfactory for the purposes of the present invention. Continuous transmission, as proposed by Castellon leads to rapid battery depletion, and the monitoring units are cumbersome, as might be expected for fixed-site installations. Also, each system is not expected to be operated within range of a similar system, so that assigned radio frequencies and codes are only unique within the system and would cause interference or possible confusion with similar systems where the same frequencies or codes were assigned. It is however envisaged that the apparatus of the invention will be compact and portable, not only the transmitters, but also the receiver monitor part. At most only a few articles, such as a brief case and wallet or two or three children would be fitted with transmitters. The users would go about their business amongst other people, including in crowded areas where there may well be many other users of the same or similar systems.

[0006] It is an object of the invention to provide a security alert apparatus which is compact and easily portable, which can be rapidly transferred to protect different items according to the user's varying daily needs and circumstances, and which overcomes the potential problems of size, interference of code confusion arising from use of several such apparatuses in proximity which would arise from such use of prior art devices.

[0007] According to the invention, the security alert apparatus comprises, at least one transmitter unit, mounted in, on, or in relation to a target to be monitored, and a receiver unit adapted to be easily carried, or worn by a user, characterised in that the or each transmitter is arranged to transmit a pseudo-unique identification code in bursts, and is inoperative between bursts, and in that the pseudo-unique identification code is a randomly generated code which is set in read only memory in the transmitter during manufacture.

[0008] The identification code may be a multi-bit digital code, for example a 20-bit code will provide for over 500,000 possible codes, and a 21-bit code over 1,000,000 or a 24 bit code will provide for over 16,000,000 possible codes. Accordingly, the risk of units having target identification codes which are identical being used within range of each other is extremely small and can be eliminated completely.

[0009] The transmitter may be arranged to transmit bursts at intervals of 3 to 4 seconds, for a period of 20-30msec. It is thus unlikely that two transmitters will be transmitting at the same moment on more than one occasion.

[0010] The transmitter unit is small, compact and lightweight and may be built into or fixable to an article such as a brief case, purse or wallet, lap top computer, or the like, or wearable as a bracelet, necklace, or sewn into a garment.

[0011] The receiver may have a timer which is re-set each time the receiver detects a signal from the transmitter. If the signal is absent for longer than a pre-set time period, say 5 seconds (slightly longer than the transmission burst repeat time) the timer may activate an alarm stage, which may in turn operate an audible or visual alarm.

[0012] Loss of signal may be due to attenuation as the transmitter is moved away from the receiver and the signal falls below a detectability threshold (the range may be extremely limited, say 4 to 5 metres), or may occur if the transmitter becomes enclosed in a predominantly metal environment such as a car, without the receiver.

[0013] The receiver may contain a programme which allows the receiver to learn the code or codes transmitted by one or more transmitters in an initialising stage, and store the code or codes.

[0014] Two preferred embodiments of the invention will now be described by way of example, with reference to the accompanying drawings, which is a block diagram showing the common features of the embodiments.

[0015] A security alert apparatus according to the invention comprises one or more transmitter units 10, which may be fixed to or built into or encapsulated in a target, and a receiver unit 11, which is compact and adapted for example to be carried in a user's pocket.

[0016] Each transmitter and receiver unit is powered by a compact power source, such as a readily available lithium battery (not shown).

[0017] The transmitter unit 10 comprises a timer 12 which operates to activate a narrow band radio frequency transmitter 13 for 20 to 30 mili-second bursts at intervals of a few seconds, in the range of 2 to 5 seconds for example. The signal is modulated by an identification code which is encoded in EPROM 14 during manufacture. The code is a randomly generated 20 or 21 bit pseudo-unique digital code, with a 500,000 or 1,000,000 to 1 duplication risk. The transmitter range is preferably limited to a few metres.

[0018] The receiver unit 11 comprises a radio frequency receiver 15 which is tuned to the narrow band frequency of the transmitter 13. The receiver contains a programme that allows it to learn the codes transmitted by the transmitters in an initialising stage, and store them in normal use; the receiver picks up the codes sent by the transmitters and compares them to the stored values.

[0019] If the code is recognised, a timer 17 is re-set. If no signal bearing the correct code is received within a preset interval, which may be the same as or slightly longer than, or a multiple of the transmitter burst interval, on alarm stage 18 is activated, and this operates a visual alarm such as LED 14, and/or an audible alarm such as a buzzer or beeper 20.

[0020] In a first version, of the apparatus, the receiver is matched with only one protected item. The apparatus additionally includes an on/off switch, and an acknowledge or cancel button to turn off the alarm once it has been noted. The transmitter/detector range is not variable, and the pre-set period for signal transmission bursts, and for enabling the alarm is 3 seconds. The batteries may be rechargeable rather than disposable. The device has a fail safe capability if outside influences reduce the detection range.

[0021] This is suitable for general use, for monitoring a single valuable article, and may be adapted somewhat for monitoring a child, by for example reducing the burst interval and alarm trigger time to two seconds. A badge may be provided to be worn by the child declaring the child to be monitored by the apparatus, which badge may contain the transmitter.

[0022] In a second version, the apparatus may be adapted to monitor two or more items from the same receiver. Each item has its own code, whilst all recognition codes are built into EPROM in the receiver unit. The transmitter may be operated alternatively, at 4 second intervals, and the trigger period for absence of a signal may be set at 3 seconds. The alarm display may be arranged to display which transmitter has defaulted. The alarm distance range may be user-variable via a switch on the receiver unit.

[0023] The invention provides for a compact easily personally transportable security apparatus which can be used to monitor valuable possessions, or children, and give almost instant warning of mislaying the article, the straying of a child, or attempted theft or abduction, and overcomes the features of the prior art which makes such devices unsuitable for the purposes envisaged.

[0024] Variations may be made within the scope of the invention, in particular to extend the capability of the receiver unit to monitor greater numbers of transmitters, the specific size and shape of transmitter for use within or on specific items of valued equipment and in detection ranges and transmission intervals, alarm trigger periods and the like.

[0025] It is of course to be understood that the invention is not intended to be restricted to the details of the above embodiment which are described by way of example only.

Claims

1. Security alert apparatus comprising, at least one transmitter unit (10) mounted in, on, or in relation to a target to be monitored, and a receiver unit (11) adapted to be easily carried by a user, characterised in that the or each transmitter unit (10) is arranged to transmit a pseudo-unique identification code in bursts, and is inoperative between bursts, and in that the pseudo-unique identification code is a randomly generated code which is set in read-only memory (14) in the transmitter (10) during manufacture.

2. Security alert apparatus according to claim 1, characterised in that the receiver to learn the code or codes transmitted by one or more transmitters (10) in an initialising stage and has a memory unit (16) to store the code or codes for comparison with codes transmitted by the or each transmitter unit (10).

3. Security alert apparatus according to claim 1 or 2, characterised in that the transmitter (10) is arranged to transmit bursts at intervals of from 3 to 4 seconds, each for a duration of from 20 - 30m sec, and is non-transmitting between busts.

4. Security alert apparatus according to claim 3 characterised in that the receiver unit (11) has a timer (17) which is reset each time the receiver detects a signal from the transmitter, and is operative to activate an alarm stage (18) of the signal is absent for a predetermined period which is longer than the transmission burst repeat time.

5. Security alert apparatus according to any preceding claim, wherein the transmitter unit (10) is built into or fixable to an article such as a briefcase, purse, wallet, laptop computer or the like, or can be worn as a bracelet or necklace or sewn into a garment.

6. Security alert apparatus according to any preceding claim, characterised in that the identification code is a multi-bit digital code, which is a randomly generated pseudo-unique code of at least 20 bits.

Drawing