Abstract:
An alarm for detecting radiation and/or pollutants such as smoke, carbon monoxide or the like has a housing, a mounting plate for mounting the housing to a flat surface, cooperating means on the housing and the mounting plate engageable to secure the housing to the mounting plate, and an alarm circuit including a detector for detecting the radiation and/or pollutants. The alarm also has a switch in the alarm circuit in the housing and a magnet on the mounting plate, the arrangement being such that the magnet actuates the switch in response to engagement of the housing with the mounting plate thereby to arm the circuit. A battery compartment in the housing receives a battery for the alarm and stop means prevent proper engagement of the cooperating means in the absence of the battery. The mounting plate is generally planar having an upper surface and a through-opening for receiving a fixing such as a screw for fixing the mounting plate to a generally flat surface. The through-opening is elongate having an enlarged portion for passage of the head of the fixing through the through-opening, a narrowed portion for retention of the head and a neck portion therebetween. The alarm circuit also preferably includes actuation means configured to scroll through the various functions of the alarm when the actuation means is activated in a particular fashion.

Description:
BACKGROUND OF THE INVENTION 
       [0001]    1. Field of the Invention 
         [0002]    This invention relates to an alarm for detecting radiation, carbon monoxide, smoke and/or other air pollutants comprising particularly for use in a household environment. 
         [0003]    2. Description of the Prior Art and Related Information 
         [0004]    A typical conventional alarm is battery-powered and is intended to be fitted directly to a flat surface, such as a ceiling, by means of screws or the like which pass through the housing of the alarm. The alarm is usually provided with a removable cover, or a cover that pivots away to the side so that access can be gained to the housing interior to change the battery. The battery is commonly mounted by simply clipping onto a terminal pad. 
         [0005]    Therefore the user can close the cover without a battery in place. In addition, because the battery is normally clipped onto a terminal holder it can easily be mounted in the wrong orientation. Both of these conditions provide a false sense of security to people seeing the alarm and believing it to be operational when in fact it is not. 
         [0006]    In addition where the alarm is a multi functional device there are usually one or a number of buttons for the different functions and operations of the alarm and the user may have difficulty in operating the alarm. This problem is present when the alarm is new as few people tend to read instruction manuals. The problem is exacerbated when dealing with a second user of an alarm where it is likely that the manual has been misplaced or discarded. Consequently, if the alarm sounds and quick action is required, for example to silence the alarm, the possibility of the user removing or disabling the alarm, for example by removing the battery, are increased. 
         [0007]    The above are some of the problems that can be encountered with these types of alarms and which have an effect on the usefulness of the alarms. These all relate to the action of the user or the ability of the user to bypass the operation of the device in a deceptive and potentially dangerous manner. 
         [0008]    The present invention seeks to provide an improved alarm. 
       SUMMARY OF THE INVENTION 
       [0009]    According to an embodiment thereof, the present invention is an alarm for detecting radiation and/or pollutants such as smoke, carbon monoxide or the like. The alarm may include, for example, a housing, a mounting assembly configured to mount the housing to a flat surface; cooperating assemblies on the housing and on the mounting assembly, the cooperating assemblies being mutually engageable to secure the housing to the mounting assembly, an alarm circuit including a detector for detecting the radiation and/or pollutants, and a controller configured to control an arming of the alarm circuit, the controller comprising a switch assembly. The cooperating assemblies may be configured to actuate the switch assembly upon engagement of the housing with the mounting assembly to thereby cause the controller to arm the alarm circuit. 
         [0010]    The switch assembly may include a magnetically operated switch and the cooperating assemblies comprise a magnet assembly. The magnet assembly may include a permanent magnet. The switch assembly may be configured to control a supply of power to the alarm circuit. The switch assembly may include a normally open switch in a power supply line for the alarm circuit. 
         [0011]    According to another embodiment thereof, the present invention is an alarm for detecting radiation and/or pollutants such as smoke, carbon monoxide or the like. The alarm may include a housing, a mounting assembly configured to mount the housing to a flat surface, cooperating assemblies on the housing and on the mounting assembly, the cooperating assemblies being mutually engageable to secure the housing to the mounting assembly; a locator configured to house a battery for the alarm, and a stop assembly configured to prevent proper engagement of the cooperating assemblies in the absence of the battery in the battery housing. 
         [0012]    According to further embodiments, the stop assembly may be configured to be biased towards a first, stop position that prevents proper mutual engagement of the cooperating assemblies in the absence of the battery in the locator and may be further configured to be displaced into a second, release position by correct insertion of the battery in the locator to thereby enable proper mutual engagement of the cooperating assemblies to secure the housing to the mounting assembly. The cooperating assemblies may be mutually engageable by rotation of the housing relative to the mounting assembly to secure the housing to the mounting assembly. The cooperating assemblies may include a retaining assembly on one of the housing and the mounting assembly and an engagement assembly on the other one of the housing and the mounting assembly. The retaining assembly may include at least one hook-like member and the engagement assembly may include a respective flange engageable under the hook-like member by rotation of the housing relative to the mounting assembly. A plurality of the cooperating assemblies may be angularly spaced about an axis of rotation of the housing and the mounting assembly. The retaining assembly may be provided on the housing and the engagement assembly may be provided on the mounting assembly. The locator may include a battery compartment and the stop assembly may include a battery sensing member on the mounting assembly extending over the battery compartment and downwardly towards the housing, and an abutment on the housing. In the absence of a battery in the battery compartment, the battery sensing member may abut the stop on relative rotation of the housing relative to the mounting assembly to prevent proper engagement of the cooperating assemblies and in the presence of a correctly inserted battery in the battery compartment, the battery sensing member may be biased away from the housing so as to clear the stop on relative rotation of the housing relative to the mounting assembly and allow proper engagement of the cooperating assemblies. The battery sensing member may include a tongue-like member. 
         [0013]    An additional abutment may be provided that may be engageable with the battery sensing member on relative rotation of the housing and the mounting assembly to prevent proper engagement of the cooperating assemblies when the mounting assembly and the housing are incorrectly aligned. At least one of the abutment and the additional abutment may include an end wall of a recess in the surface of the housing. The recess may have a ramp-like base. The locator may include a battery compartment that may be configured to prevent incorrect insertion of the battery into the compartment. The battery may be of a type having positive and negative terminals of different sizes at one end, and the battery compartment may include electrical contacts at one end thereof for connection to the terminals of the battery, and the battery compartment may be configured, on the end wall, to prevent insertion of the battery with the terminals transposed. The battery compartment may be further configured to define a recess in the end wall for receiving a smaller one of the positive and negative battery terminals, the defined recess being too small to receive a larger one of the positive and negative battery terminals. 
         [0014]    The advantage with this arrangement relates to the fact that the housing must be demounted from the mounting means to change the battery and cannot be remounted without a battery being in place. This prevents mounting of the device without a battery. Further, with this arrangement the battery may only be fitted when it is the correct battery and in the correct orientation so preventing incorrect mounting of a battery in the device that could lead to malfunctioning or damage to the device. 
         [0015]    According to a still further embodiment, the present invention is an alarm for detecting radiation and/or pollutants such as smoke, carbon monoxide or the like, comprising a housing; mounting assembly for mounting the housing to a flat surface; cooperating assemblies on the housing and on the mounting assembly, the cooperating assemblies being mutually engageable to secure the housing to the mounting assembly, and an alarm circuit including a detector configured to detect the radiation and/or pollutants. 
         [0016]    The mounting assembly may include a generally planar mounting plate having an upper surface and a through-opening for receiving a fixing such as a screw for fixing the mounting assembly to a generally flat surface, the through-opening being elongate and having an enlarged portion for passage of a head of the fixing through the through-opening, a narrowed portion for retention of the head and a neck portion therebetween. The neck portion may define a wall portion, the wall portion being formed by a tongue, the tongue being adapted to resile away from the opposing wall of the neck portion thereby to allow passage of the fixing from the enlarged portion to the narrowed portion, and to prevent passage of the fixing from the narrowed portion to the enlarged portion. 
         [0017]    A still further embodiment of the present invention is an alarm for detecting radiation and/or pollutants such as smoke, carbon monoxide or the like comprising a housing; mounting assembly for mounting the housing to a flat surface; cooperating assemblies on the housing and on the mounting assembly, the cooperating assemblies being mutually engageable to secure the housing to the mounting assembly, and an alarm circuit, the alarm circuit including a detector configured to detect the radiation and/or pollutants. The alarm circuit may include an actuation assembly configured to scroll through various functions of the alarm when the actuation assembly is activated in a predetermined fashion. 
         [0018]    The alarm circuit may include a microprocessor configured to control an operation of the alarm, the actuation assembly may include a switch in the alarm circuit, and the alarm circuit may be configured such that when the alarm is activated, actuation of the switch silences the alarm and configured such that, when the alarm is silent, actuation of the switch tests the alarm. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0019]    The invention will now be illustrated by way of description of an example of the present invention, with reference to the accompanying drawings, in which: 
           [0020]      FIG. 1  shows a side view of an alarm in accordance with the present invention; 
           [0021]      FIG. 2  shows a plan view of an upper housing member of the alarm shown in  FIG. 1  with the battery omitted; 
           [0022]      FIG. 2   a  shows a perspective view of the upper housing member from above; 
           [0023]      FIG. 3  is a plan view of a mounting plate of the alarm of  FIG. 1 ; 
           [0024]      FIG. 4  is an inverse plan view of the mounting plate of the alarm of  FIG. 1 ; 
           [0025]      FIG. 5  is a circuit diagram of part of the circuitry of the alarm of  FIG. 1 ; 
           [0026]      FIG. 6  is an inverse plan view of the upper housing member with component parts attached; and 
           [0027]      FIG. 7  is a view from below of a lower housing member of the alarm. 
       
    
    
     DETAILED DESCRIPTION 
       [0028]    Reference will now be made in detail to the construction and operation of preferred implementations of the present invention illustrated in the accompanying drawings. The following description of the preferred implementations of the present invention is only exemplary of the invention. The present invention is not limited to these implementations, but may be realized by other implementations. Indeed, In the below-described embodiment, the invention is described in relation to a smoke alarm. It will be appreciated, however, that the invention is equally applicable to an alarm for detecting other air pollutants and noxious and toxic gases such as carbon monoxide, radon or the like, or any forms of radiation. 
         [0029]    Referring to the drawings,  FIG. 1  shows a side view of a preferred form of alarm  1  according to the invention. The alarm is suitable for mounting to a flat surface such as a wall or ceiling but is described here in relation to its mounting to a ceiling. Certain aspects of the present invention to be illustrated include design detail of the alarm and this will now be described in detail. 
         [0030]    The alarm  1  comprises a housing and a mounting means for mounting the housing to the ceiling. The mounting means is in the form of a mounting plate  2  which is generally circular and planar. The housing has an upper housing portion or member  3 , and a lower housing portion or member  4 . The terms upper and lower are relative and depend on the orientation of the alarm but are used here in the sense that applies where the alarm is attached to a ceiling and as shown in  FIG. 1 . 
         [0031]    The illustrated alarm is circular with a domed construction to give an aesthetically pleasing appearance. 
         [0032]    The lower housing member  4  has a generally circular, domed construction with a substantially smooth outer surface  90  and rim  92 . When the alarm is mounted to a flat surface this housing member  4  will be furthest from the flat surface. In the case of mounting to a ceiling, for example, the housing member  4  will face the floor. The member  4  includes, a “test function” and “silence” button  5  (the only button provided with this design of alarm) which is located at or near the apex of the dome. The housing member  4  also has a group of vents  6  (typically 5) in the surface of the dome just below the button  5 . A speaker is mounted adjacent the vents  6  inside the housing of the alarm. 
         [0033]      FIG. 2  is a plan view (i.e. from above) of the upper housing member  3 . The upper housing member  3  is generally circular and includes a generally planar base in the form of a bottom or base plate  7  with an outwardly and downwardly angled sidewall  50  extending the full periphery. The sidewall  50  has a number of openings  8  spaced around the circumference of the base plate  7 . These are preferably equi-angularly spaced along the sidewall  50  although any suitable spacing may be used. Alignment means in the form of a detent or slot  8   a  is provided in the sidewall  50  and its purpose is explained below. The openings  8  provide ventilation for the operating circuitry and also better enable the alarm to be heard when it is sounding. 
         [0034]    The lower housing member  4  and upper housing member  3  are preferably snap-fitted together by catch means preferably in the form of cooperating lug and receptor assemblies  9 . In this example there are three assemblies  9 . The lugs are preferably formed on the lower housing member  4  and the receptors on the upper housing member  3  although it will be appreciated that these may be reversed. It will also be appreciated that more or fewer than three assemblies may be used and these are preferably equi-angularly spaced around the housing. 
         [0035]    In this example of the present invention there are three lug and receptor assemblies  9  spaced apart in a particular orientation about the respective surfaces of the housing members  3  and  4  and the spacing of these arrangements is such that the two housing members will only snap together in one particular alignment. Each lug (not shown in the drawings) is upstanding on the inner surface of the lower housing member  4  and is formed with a hook-like end portion. This engages in a snap-fitting manner over a shoulder formed on the corresponding receptor. The latter is upstanding on the inner (lower) surface of the upper housing member  3 . 
         [0036]    When the housing members  3  and  4  are snapped together a space is defined therebetween in which the circuitry, speaker and other active components of the alarm can be housed. Suitable mounting means are provided for the mounting of these to the upper housing member  3  or the lower housing member  4 . 
         [0037]    The upper housing member  3 , also includes the following:
   a circumferential groove  10  at or adjacent the outer edge of the base plate  7 . This is formed in the upper surface  80  of the base plate  7  as can be seen in  FIG. 2   a;      a battery locating means in the form of a battery compartment  11  which is formed as a well or recess in the upper surface of the base plate  7  and extends into the interior of the upper housing member  3 ;   retaining means  12  forming part of cooperating means for securing the upper and lower housing members together. Here, the retaining means  12  are in the preferred form of three hook-like members  12  equally spaced around the base plate  7 . Although three members  12  are shown it will be appreciated that any suitable number may be used; and   a locking means  15  adjacent the outer periphery of the plate  7 .   
 
         [0042]    In the particular example shown in  FIGS. 2 and 2   a  the battery compartment is sized and suited for the location and housing of a battery of the type having positive and negative terminals of different sizes at one end, such as a 9V PP3 battery. The battery compartment therefore comprises a generally rectangular well  62  having two end walls  54 , two side walls  58  and a base  60 . Means (not shown) are provided at one end for the location of terminals to connect the battery in the compartment  11  to the circuitry of the alarm. 
         [0043]    Battery contact terminals of the alarm circuitry are located in designated terminal fixing points  63 ,  65  provided on the right hand end wall  54  of the well as seen in  FIG. 2 . The fixing points are defined by vertical side struts  16  disposed one adjacent each end of the end of the well and a centre strut  17  at a position offset from the centre of the respective end of the well. The struts  16  &amp;  17  extend down the full depth of the well and project outwardly into the well to define recesses in the end wall  54 . The terminals are located between the struts in the recesses so that the terminals are shielded from side access in the well  62 . This means that the terminals will only be contacted when the correct battery is correctly inserted. The battery is fitted into the battery compartment from the outside of the upper housing member  3  i.e. from above as seen in  FIG. 2 . the spacing between one of the side struts  16  and the intermediate strut  17  is wide enough for the smaller of the two battery terminals but smaller than the larger battery terminal. This ensures that the battery cannot be incorrectly connected in the compartment  11 . 
         [0044]    As can be seen in  FIGS. 2 and 2   a  the base  60  of the well  62  has a tongue  18  which is cut out of the base  60  and extends centrally across the width of the well  62 . The tongue  18  is sprung slightly so that it extends out of the plane of the base  62  towards the lower housing member  4  and is generally L-shaped, having an arm  96  which extends upwardly. The tongue  18  is located above the button  5  so that as the button  5  is depressed the arm actuates a switch SW 1  of the alarm circuit  70 . The tongue  18  is preferably mechanically coupled to the button  5  although it can simply be in abutment. 
         [0045]    The alarm has cooperating stop means on the upper housing member  4  and the mounting plate  2  which includes three arcuate indents or recesses  13 ,  14 ,  19  in the base plate  7 . The arcuate indent  19  is provided in the base plate  7  adjacent one side wall  58  of the well  62  close to the edge of the plate  7 . The first and second indents  13  and  14 , and the indent  17  are equi-angularly spaced around the outer surface region of the base plate  7  of the upper housing member  3 . The indents  13 ,  14  also have a ramp-like base  98  ending in a stop or wall  99 . 
         [0046]    The cooperating stop means on the mounting plate  2  is a battery sensing member in the preferred form of a cut-out tongue-like member  28  that is sprung out of the surface of the plate  2  towards the upper housing member  3 . On the inner (lower) side of the tongue  28  there is a domed or raised portion  29 . In its normal position the tongue  28  is orientated to protrude downwardly from the inner surface of the mounting plate  7  into the battery compartment  11 . 
         [0047]      FIGS. 3 and 4  show the two sides of the mounting plate  2  which is suitable for mounting the alarm to a flat surface.  FIG. 3  shows the external, upper surface  2   a  of the mounting plate which is in contact with the surface to which the alarm is mounted, and  FIG. 4  shows the internal, lower surface  2   b  which faces the upper housing member  3 . The mounting plate  2  comprises a substantially flat disc-shaped member of similar diameter to the diameter of the housing base plate  7 . 
         [0048]    The upper surface  2   b  is provided with three smooth surface mounting projections or nodules  64  that engage the ceiling and hold the major part of the surface of the mounting plate away from the ceiling surface. 
         [0049]    The mounting plate  2  includes a centrally located fixing through-opening or hole  20  which enables the mounting plate  2  to be fixed to the ceiling by, for example, a dry wall fixing. This allows fixing in one operation and without drilling. This in turn means that the risk from asbestos, where present, is reduced or removed. The fixing hole  20  is keyhole shaped having a central, generally circular or narrowed portion  21  and a bulbous extension or enlarged portion  22  which forms a neck portion  23  where the bulbous extension  22  meets the central portion  21 . A cut out sprung arm or tongue  24  is formed in one side wall of the bulbous portion  22 . The tongue  24  forms a locating portion which resiles away from the fixing means when the latter is located in the bulbous section and slid up into the portion  21 . Once the fixing means enters the central portion  21  the tongue  24  resiles back towards its original position, locking the fixing means securely in place in the central portion  21 . 
         [0050]    The mounting plate  2  also includes three engagement means  25 . These engage with the retaining means  12  and thus form part of the cooperating means mentioned above for locking the mounting plate  2  to the upper housing member  3 . The engagement means  25  are also equally spaced around the circumference of the mounting plate  2 . Each engagement means  25  comprises an opening  26  of arcuate shape in the mounting plate  2  with a flange  27  formed on the lower surface  2   a  of the mounting plate  7 . The flange  27  extends over part of the length of the opening from one end thereof and over part of the width. The flange  27  includes a chamfered end section  27   a  at its free end and a portion of reduced thickness at its other end. 
         [0051]    A marker  31  is also provided in the mounting plate  2  adjacent the edge of the plate. This marker is conveniently a cut-out portion which is visible from the underside of the plate  2 . A raised lip or ridge  32 , conveniently extending along the periphery of the plate  2 , is also provided on the lower surface  2   a  at or adjacent the edge of the mounting plate  2 . 
         [0052]    In use, the mounting plate  2  is first fitted to the ceiling, for example by means of a dry wall fixing. The fire alarm upper housing member  3  is then mounted to the mounting plate  2 . In order to achieve this the marker  31  on the plate  2  is aligned with the detent  8   a  in the sidewall  50  of the upper housing member  3  but at a slightly offset angle (anti clockwise). This ensures that the upper housing member  3  fits against the mounting plate correctly and the raised lip  32  on the mounting plate  2  slots into the groove  10  of the upper housing member. In this position, the chamfered end section  27   a  of each flange  27  is aligned to one side of a respective hook-like member  12 . If a battery is located in the battery compartment  11 , when the upper housing member  3  is presented to the mounting plate  2  properly aligned, the tongue  28  is orientated to protrude downwardly from the inner surface of the mounting plate  7  into the battery compartment  11 . The portion  29  of the tongue  28  thus engages the surface of the battery and the tongue  28  is upwardly displaced above the surface of the upper housing member  3 . 
         [0053]    As the fire alarm upper housing member is then rotated in a clockwise direction to locate the housing with respect to the mounting plate  2  each of the respective flanges  27  engages under the respective hook-like member  12  in a sliding action and, assuming certain other factors discussed below are met, the fire alarm can be rotated until the marker  31  is aligned with the detent  8   a  and the fire alarm is correctly mounted. 
         [0054]    If there is no battery in the battery compartment  11  then the tongue  28  is not upwardly displaced as the fire alarm housing is presented to the mounting plate  2 . The tongue  28 , therefore, extends into the well  62  of the battery compartment. As the housing is rotated, the tongue  28  engages the end wall of the indent  19 , preventing further rotation of the housing with respect to the mounting plate  2  and so preventing the alarm housing being secured to the mounting plate  2  and thus to the ceiling. 
         [0055]    Furthermore, the particular design of alarm housing shown in the drawings has only three possible positions for mounting to the mounting plate  2 . The correct position is as described above where the marker  31  is lined up relative to the detent  8   a  and the tongue  28  is engaged by the battery to allow fixing of the fire alarm to the mounting plate  2  and therefore the ceiling. In the event that an attempt is made to mount the device to the mounting plate  2  in either of the other possible positions (two with this example) the tongue  28  will locate in either the first or second indents  13 ,  14 . Therefore as the alarm housing is rotated (no matter whether a battery is fitted or not) the tongue  28  will engage the end wall of the respective indent  13 ,  14  and again prevent securing of the alarm housing to the mounting plate and therefore the flat surface. 
         [0056]    If an attempt is made to fit a battery incorrectly in the battery compartment  11 , the battery will not sit fully in the compartment and will sit proud, thus preventing the upper housing member from being secured to the mounting plate  2 . 
         [0057]    The above describes an example of an alarm which includes safety features to ensure that the alarm may only be assembled when the correct battery is correctly fitted, and also to ensure that the battery is wired and connected correctly, so ensuring that when the alarm is fitted the alarm is operational (assuming that the battery carries a charge). 
         [0058]    The following refers to a further preferred embodiment of alarm according to the invention. In this embodiment a magnet  100  is fitted into an indent provided in the lower surface  2   a  of the mounting plate  2 . In the example shown this is located close to the marker  31 . 
         [0059]    In addition a hook means may be provided on the lower housing member  3  so that if the magnet is not present then the hook would locate in the indent provided in the mounting to prevent rotation of the housing on the mounting plate  2  and thus assembly of the alarm housing to the mounting plate  2 . A reed switch  101  is located in the housing, on the lower housing member  3  in the vicinity of the indent  8   a  but on the inner (lower) surface. 
         [0060]    The normal condition for the reed switch is open, preventing energizing of the alarm. When the alarm housing is properly fitted to the mounting plate  2 , the reed switch  101  is located in the vicinity of the magnet. The magnetic field of the magnet moves the reed switch to the closed position, allowing power to be supplied to the alarm circuitry by the battery. 
         [0061]    This means that the circuitry will only be armed when it has been fitted to the mounting plate. Therefore, unless the mounting plate is not itself fitted to a flat surface, this means that the alarm will only be active in situ. 
         [0062]    The advantages with this arrangement result from the fact that the switch unit is a hermetically sealed unit and that with the mount and demount there is an automatic on/off switch. This second aspect of the invention may be use separately, or with either or both of the first and second aspects of the present invention. 
         [0063]    Turning now to the circuit of  FIG. 5 , alarms of various types are frequently used by persons without a useful knowledge of their operating principles. They consequently may not be capable of using the alarms correctly or in the best way. This is particularly true if an alarm has more than one function, which may be initiated by one or more user operated controls. Operation of multiple functions is frequently dependent on the user reading the instructions in a user manual and in practice this does not always happen. Even when the manual has been read thoroughly, the user may not remember the operating sequences when needed. The nature of an alarm is generally such that quick action is required, so there may not be sufficient time to re-read the manual or a quick operation is desired (to silence an alarm, for example). Commonly, the inability of the user to generate the required response from the alarm may result in its being removed and/or reported as being faulty, or the alarm disabled in some way (e.g. by removing a battery). The protection provided by the alarm is then removed. 
         [0064]    A proposed solution to this problem is to minimize the number of user operated controls and to make their operation intuitive. Most users will normally only want and expect a limited number of reactions from their alarms. By minimizing the options available to the user and making the alarms react to simple operations, there is a greatly reduced dependency on learning written instructions. The likelihood of disabled alarms and reported nonexistent faults will consequently be much lower. 
         [0065]    This principle can be applied to any number of functions on an alarm. In particular though, many alarms have only two main functions that a user will want to access; testing the alarm, and silencing the alarm. This applies generally to all alarm types. 
         [0066]    Of the two functions described above, only one function will be required at any particular time, dependent on the operating state of the alarm. When the alarm is silent, the only function required will be “test”; when it is in alarm, the only function required will be “silence”. There is consequently no need to have more than one external control, as the switch function can be determined by the operating condition of the alarm. 
         [0067]    This single control could take a number of different forms such as a switch, external light source (e.g. a torch), or any other method that can be user initiated. 
         [0068]    In the above described embodiments the particular solution is to use a pushbutton switch on the alarm. Some existing alarms use a single pushbutton switch to control two functions, but these may operate both functions in sequence, depend on the switch being held for time periods specific to function, require the switch to be operated a certain number of times, or in some other way, require an action on the user that is not intuitive. 
         [0069]    The proposed solution uses the alarm condition to determine how it will react to the operation of the switch. When the switch is operated, there is only one reaction required for the prevailing operating conditions. There is therefore no requirement for any complex analysis of the timing of the switch. It is either being pressed or it is not. The circuit could be designed, using electronics or software, to respond simply whenever the switch is operated for a minimum time (typically under a second). 
         [0070]    From the user&#39;s perspective, when the alarm is silent he may want to test it. Only one control (pushbutton switch) is visible, so he presses this. The alarm goes into “test”. The user&#39;s reaction would typically be to release the pushbutton either instantaneously (before the alarm goes into “test”) or after hearing it going into “test”. The “test” cycle would last long enough to ensure it is audible to the user in either case. 
         [0071]    If the alarm is in “full alarm” mode, the user may want to silence it. Again, only one control is visible so he presses this. The alarm goes into “silence” mode. 
         [0072]    The alarm includes a single button which is configured to scroll through the various functions of the alarm when the button is activated in a particular fashion. 
         [0073]    With this configuration when the button is activated there will be a reaction to the prevailing condition and there is no need for any detailed analysis. Further if the alarm is in a non-reacting mode, and therefore silent the pressing of the button will activate the test circuits of the alarm/detector. 
         [0074]    This solution does not preclude the initiation of multiple functions by other means in addition to a single control button. For example, an alarm connected to an electric lighting circuit could be controlled by counting the number of times that the light switch is flicked in a short time. 
         [0075]      FIG. 5  shows a circuit diagram  70  for the preferred embodiment of alarm which provides the above described single switch function. The circuit has a microprocessor  72  which controls operation of the alarm in dependence on the sensed input from the smoke/pollutant detector  74 . A switch SW 1  is connected in a line between the collector-emitter junction of two series connected transistors Q 1   b,  Q 1   a  and a terminal of the microprocessor, and is actioned by pressing the button  5  on the alarm housing. When switch SW 1  is pushed (closed) and the alarm is off the emitter of Q 1   b  is taken towards ground and the transistor Q 1   b  is switched on, as is Q 2 , and the detector  74  is pulled low into an alarm state. 
         [0076]    When the alarm is on and SW 1  is pushed, Q 1   a  is switched on which triggers the silence function on pin 1  of microprocessor  72 .