BACKGROUND TO THE INVENTION It is common in present day smoke alarm units to incorporate a power supply derived from the standard mains supply, for example 240V a. c., an internal backup battery for example a 9V d. c. battery, a smoke detection sensor unit, typically of photoelectric or ionisation design, and a sounder. Such units provide terminals for connection of the mains supply.

Typically in large buildings there may be several different types of detection apparatus, such as smoke detectors and heat detectors, as well as alarm apparatus interconnected to an alarm supervisory board. Such a board will typically monitor the detectors throughout the building and upon locating a positive detect signal, the board will appropriately activate the alarm apparatus.

A typical alarm apparatus in apartment buildings consists of sounders in the buildings corridors connected to the supervisory board. Such an alarm system, however, may only be activated via the centralised control of the alarm supervisory board. Such supervisory panels include expensive apparatus and are generally expensive to install and maintain. The system is also complex and inflexible as all instructing communications are initiated by the supervisory panel.

An additional problem that confronts the designer of a fire alarm system is that it is highly desirable that in large buildings, particularly apartment buildings, the alarms be activated, not only where the fire is initially detected but throughout the entire building so that the occupants in their own occupancy, rooms or units will have the necessary early warning. The early warning provides for additional time to evacuate the building. As typical warning system in apartment buildings consists of sounders in the buildings corridors connected to a supervisory board, the system is not always effective in alerting the building's occupants, particularly if they are sleeping, due to the sounders being

external to the occupant's room or unit.

US Patent No. 5,587,705 addressed these problems by providing a smoke detector that operates with other smoke detectors of the same design by communicating an alarm directly to other smoke detectors, without the need of an intermediary fire supervisory panel. In this patent, communication is initiated by a detector which senses smoke. That detector sounds its own alarm and sends a radio signal of a certain frequency to other nearby detectors tuned to that frequency. The detectors that receive the radio signal emit a pulsed alarm to act as an early warning system for occupants of the building remote from the initiating smoke detector. This system, while attaining decentralised control still lacks a degree of flexibility, particularly since only detectors within radio receiving distance are able to be simultaneously sounded, and also because the detectors are only able to communicate with other compatible detectors.

This last point means that there would be considerable expense to installing such detectors in a building, as all detectors would need to be of the same type to have an effective system.

A further problem that has hitherto arisen when using interconnected alarm units in a common area is that it is often very difficult to identify at which unit the alarm signal originated. This problem is also relevant to the situation of identifying a nuisance alarm which is overly sensitive and prone to generating false alarms.

A further problem that confronts the user of a plurality of smoke alarm units is that the status of the back-up battery in each unit is not always readily apparent. In the past smoke alarm units have typically generated a warning chirp by means of the sounder when the battery level has fallen below a threshold level. However a problem presents itself in that it is not easy to identify which alarm unit is chirping if several are mounted in the same area.

This problem is further exacerbated for hearing impaired persons, as the chirp may not be loud enough for them to hear.

It is therefore an object of the present invention to provide an alarm unit that provides enhanced flexibility in its ability to communicate with other devices.

It is a further object of the present invention to alleviate at least one

problem of the prior art.

SUMMARY OF THE INVENTION The present invention provides an environmental condition detection alarm unit including: (a) a sensor; (b) a sounder; (c) mains power terminal connections; (d) a detect input/output (I/O) terminal adapted to interconnect with one or more other alarm units; and (e) a fourth terminal adapted to be in communicable relation with one or more external devices; wherein the sounder is adapted to be activated upon receiving an activation signal via any one of the sensor, the detect I/O terminal or the fourth terminal.

The environmental conditions that such a unit may detect include smoke, heat, movement or even a particular harmful gas.

The advantages that stem from the inclusion of the"fourth terminal", is that the detector is afforded a greater degree of flexibility in its communications.

That is, in various system configurations incorporating the detector units, the units are able to receive initiating signals from an external source as well as other detectors. Examples of external sources which are able to initiate a signal to the smoke alarm units are a compatible sprinkler system or even an alarm supervisory board. In the example of the detectors being in communicable relation with the alarm supervisory board it is possible to gradually introduce these detectors into a buildings detector system and still remain compatible with other detectors, as the board could act as an intermediary.

A further advantage is that the fourth terminal may be used as an output to operate external devices, such as an additional external strobe or siren.

According to a further aspect of the invention there is provided a smoke alarm unit including: a) a backup battery; b) a battery condition detector; c) a visual indicator;

characterised in that upon the battery condition detector detecting a poor battery condition it will activate the visual indicator.

According to a further aspect of the invention there is provided a method for detecting the originating alarm unit in a plurality of interconnected alarm units, each alarm unit including visual and audible alarm indicators, including the steps of: a) upon detecting an alarm signal in an originating alarm unit, activating the audible alarm indicators in each of the plurality of alarm units and the visual alarm indicator in the originating alarm unit; b) upon sensing the cessation of the alarm signal, deactivating the audible alarm indicators in each of the plurality of units; and c) maintaining activation of the visual indicator in the originating alarm for a period of time.

BRIEF DESCRIPTION OF THE FIGURES Figure 1 depicts a block diagram of a smoke alarm unit according to an embodiment of the present invention.

Figure 2 depicts the interconnection of three smoke alarm units the same as the one shown in Figure 1.

Figure 3 depicts a first arrangement of three smoke alarm units the same or similar to the one shown in Figure 1, and an alarm supervisory board.

Figure 4 depicts a second arrangement of the three smoke alarm units and an alarm supervisory board.

DETAILED DESCRIPTION Referring now to Figure 1 there is depicted a schematic diagram of a smoke alarm unit according to a preferred embodiment of the present invention.

Mains power enters power converter 5 at active terminal 1 and neutral terminal 3. The power converter converts the mains power to approximately 10V on power rail 15 which is used to power the alarm unit. Green LED 17 is connected to power converter 5 and lights when said converter is operating normally to visually indicate that the AC mains power is connected and the smoke alarm unit is operational. The unit includes a disposable backup battery 7 which is connected to battery monitor module 13 and to the anode of diode 11.

The cathode of diode 11 is connected to the output of power converter 5. By virtue of the connection of backup battery 7 via diode 11 to power rail 15 the battery provides a power backup in the event that mains power or power converter 5 fails.

Battery monitor module 13 is further connected to yellow LED 19 which is lit by battery monitor module 13 if the voltage of battery 7 falls below a threshold level. Consequently an alarm unit with a failed backup battery may be readily identified by visually identifying the alarm unit with a lit or flashing yellow LED so that the confusion associated with the use of"chirping"to signal a low backup battery level is overcome. This feature may be used particularly with ionisation- type smoke alarms and photoelectric type smoke alarms with replaceable or rechargeable batteries. In addition, the visual indication may be used as the sole indication of the battery levels, or in conjunction with the audible"chirp" indication.

The alarm unit further includes a digital logic chip 21 which monitors the detector module 23. This detector is most preferably a smoke or fire detector, but it is equally possible that the detector may be used to detect other conditions, such as a particular gas or even movement. In the embodiment of the detector being a smoke or fire detector, the detector module 23 generates a signal in the event of smoke or heat being detected. The operation of detector module 23 when detecting smoke may be emulated by depressing test button 29 thereby commanding test generator 30 to send an emulated smoke detect signal to logic chip 21.

The logic chip 21 is also adapted to receive a activation signal from the detect I/O terminal 27 or the fourth terminal 4 (+9V) which signals the logic chip 21 to sound the buzzer 31 as an early warning device.

The operation of the smoke detector unit of figure 1 will now be described. Upon sensing a smoke detect signal from smoke detect module 23, logic chip 21 sets bi-directional detect 1/0 terminal 27 and fourth terminal 4 to a particular logic level (eg a potential of +9V) to indicate the smoke detect signal and accordingly the presence of a fire. Red LED 25 is then latched high so that it will not deactivate even after the smoke detector module 23 no longer

generates a smoke detect signal. The latch may be either part of alarm LED control module 24 or alternatively be incorporated into logic chip 21. Logic chip 21 also activates buzzer 31.

The buzzer continues to sound until the signal from smoke detector module 23 indicates that smoke is no longer detected, at which point logic chip 21 de-activates buzzer 31, returns detect I/O terminal 27 and fourth terminal 4 low, and sends a negating signal to alarm LED control module 24. The red alarm LED 25 remains lit for a while after the buzzer is deactivated and then automatically diminishes. Typically, LED 25 is adapted to diminish after approximately 5 minutes.

The detect I/O terminal is adapted to be connected to corresponding detect I/O terminals of other compatible alarm units. Therefore, by setting the detect 1/0 terminal of the figure 1 alarm device high when smoke is detected, any connected alarm units are notified of the detection of a fire, which results in their own alarms being initiated so as to act as an early warning alarm to occupants in other parts of the building. Conversely, the smoke alarm of figure 1 is able to receive a signal from another remote alarm unit and sound its alarm as an early warning device. These features will be discussed in more detail shortly, particularly in relation to figure 2.

The fourth terminal 4 is a terminal in addition to the detect 1/0 terminal, which is adapted to be connected to one or more external compatible devices. It may therefore notify the one or more external devices of the detection of smoke, so that they are able to respond accordingly. For example, the fourth terminal may send a signal directly to a sprinkler system in order to activate the sprinkler system. The fourth terminal may also receive signals from external devices in order to activate the alarm unit as an early warning. The fourth terminal 4 is connected to the logic chip 21, either directly, or indirectly, the latter configuration being shown in figure 1.

If the logic chip receives an activation signal from either the detect 1/0 terminal 27 or the fourth terminal 4, it activates the buzzer 31. In this situation, it is also possible that the"early warning"buzzer is different to that of the"initiating detector"buzzer, so that occupants of the building may aurally determine

whether their alarm is the initiating alarm or whether the alarm is an early warning alarm.

Figure 2 further illustrates the operation of multiple alarm units interconnected via the detect 1/0 terminal 27. The alarm units A, B, C, are the same as the alarm unit depicted in Figure 1, so the same reference numerals will be used in this description. The detect I/O terminals of all three alarm units are connected together by cable 33. In the event that a fire occurs nearest to an alarm unit, for example unit A, the smoke detector module in that unit will sense the associated smoke and generate a detect signal. The logic chip 21 A of unit A will monitor detect l/O terminal 27, find that it is floating and set it high, it will also latch red alarm LED 25A and activate buzzer 31 A. Upon the detect)/0 port 27A of logic chip 21 A being set high the bi-directional logic ports 21 B, 21 C of the logic chips in alarm units B and C respectively will also go high by virtue of their connection to cable 33. Upon the logic chips in units B and C detecting the alarm state at their bi-directional detect I/O terminals 27B, 27C, they will activate their buzzers 31 B, 31 C respectively.

Subsequently, at such time when smoke detector module 23A in alarm unit A is no longer in a smoke detect state, logic chip 21 A will return I/O terminal 27A to low, so that the connected bi-directional detect I/O terminals 27B and 27C will also fall low. The logic chips in all units also deactivate their respective buzzers. However, the alarm LED 25A in unit A will remain lit, for example for approximately five minutes, thereby indicating to an observer that it is the unit from which the first alarm signal originated. In this way the originating alarm is conveniently identified even after the alarm units have ceased sounding and without the need for complex wiring.

Such an indication facilitates an early identification of the source of the fire or alarm, resulting in a reduction in the time spent trouble-shooting, as well as the associated costs. It also enables occupants of a building to identify whether the alarm was activated within their room or apartment, whereas if it is unlit, the alarm was generated remotely. This warning diagnostic feature is able to be provided by the smoke alarm unit according to the present invention without the need for additional hardware, resulting in cost savings in equipment

and labour.

In an alternative embodiment, when smoke is detected at unit A and the logic chips in units B and C detect the alarm state at l/O terminals 27B, 27C thereby activating their buzzers, their alarm LED's 25B, 25C may also be activated, but not latched. Therefore, when the signal at the 1/0 terminals falls low, deactivating the buzzers, the alarm LED's 25B and 25C will also be deactivated leaving only the alarm LED 25A of unit A lit for a pre-determined time in order to indicate the unit which originated the alarm signal.

In Figures 3 and 4 the smoke alarm units are illustrated as integrated in a building's warning system. This is achieved through the provision of a"fourth terminal" (indicated on each unit in Figure 3 by the references 43A, 43B, 43C) and connecting these terminals either directly or indirectly to an external device.

An example of an indirect connection to an external device is via an alarm supervisory board. This configuration is illustrated in both Figures 3 and 4.

Referring now to Figure 3 there is depicted an arrangement of three smoke alarm units D, E, F of the type the same or similar to that shown in Figure 1, and an alarm supervisory board 41 interfaced to each of the alarm units by means of three normally open (i. e. open when de-energised) relays 45,46,47.

According to the present invention alarm units D, E, F, may be conveniently activated by the alarm supervisory board 41. This capability is achieved by provision of the externally accessible +9V"fourth"terminals 43D, 43E, 43F in each alarm unit.

In the event of supervisory board 41 being notified of a hazard by an external device, by means of one or more of its connections 49 for example, it may decide to activate alarm units D, E, F. Activation of the alarm units is achieved by passing a current through relays 45,46 and 47. This current energises the relay coils in relays 44,46 and 47 and so closes switches 50,51 and 52 thereby connecting detect 1/0 terminals 27A, 27B and 27C to their respective"fourth"terminals 4D, 4E and 4F. Consequently, each of alarm units D, E, F will enter an alarm state. It should be noted that none of the alarm units will latch their alarm LEDs 25D, 25E, 25F, as in a preferred embodiment, latching only occurs in an originating alarm unit and in the present case the

alarm signal does not originate in any of the alarm units.

It is to be noted that in the Figure 3 embodiment, all of the alarm units D, E, F are in parallel with the alarm supervisory board 41 and the alarm units are not interconnected (ie the)/0 detect terminals of each alarm unit are not directly connected to each other). This therefore means that the alarm units work independently as smoke alarms and will only activate simultaneously if an activation signal is sent by the alarm supervisory panel via the fourth terminals 4D, 4E and 4F. It is however to be noted that although each alarm unit D, E and F are not able to activate each others alarms as an early warning system they are all capable of sending a signal to the alarm supervisory panel 41 via relays 45,46, and 47 respectively, notifying the panel of the existence of a fire, which is in turn able to activate external devices, such as sprinkler systems or additional external strobes or sirens.

Referring now to Figure 4 there is depicted a further arrangement of a supervisory board 41 and three alarm units G, H, J. the same or similar to the unit of Figure 1. By this arrangement one relay 55 is used to interface only one alarm unit, being alarm unit G. A common wire 33 interconnects detect)/0 terminals 27G, 27H and 27J. In the event of supervisory board 41 determining that a smoke alarm condition exists it energises the coil of relay 55 thereby closing switch 57 and energising both detect 1/0 terminal 27G and the fourth terminal 4G. As a result logic chip 21 G recognises an alarm state and activates buzzer 31 G and, optionally, alarm LED 25G. As detect 1/0 terminal 27G is wired to detect 1/0 terminals 27H and 27J by cable 33, alarm units H and J similarly enter an alarm state. While each alarm unit may illuminate their alarm LEDs, none of the alarm units latch their alarm LEDs because the alarm command originates at supervisory board 41 rather than in any of alarm units G, H, J.

It is to be noted that a difference between this Figure 4 embodiment and that of Figure 3, is that the alarm units are interconnected in this embodiment.

Therefore in this example, if alarm unit G detects smoke, it activates the other interconnected detectors H and J.

Therefore, considering all of these examples and embodiments it is apparent that the combination of the 1/0 detect terminal and the fourth terminal

provides each smoke alarm with enhanced flexibility in arranging suitable configurations.

The invention is not limited to any particular form but rather it will be apparent that the details of the embodiments described above may be varied to meet different requirements. For example, the fourth terminal of the alarm unit need not be hard-wired via a relay to an external device. It may, for example be connected via a radio connection. The only requirement is that the fourth terminal is capable of being in communicable relation with one or more external device.

Further, alternative arrangements of alarm units are possible, including other configurations incorporating alarm supervisory boards or directly connected to one or more external devices.