an alarm network for a building 8 , or the like , having a plurality of audible alarms 10 disposed at various locations throughout the building is shown in fig1 . an audible alarm 10 , in this case a smoke detector , is disposed in the basement , the kitchen , the living room , the central hallway to the bedroom and in the master bedroom . even when some of the alarms are disposed on different floors of the building , and even though these alarms may be separated by closed doors , it is clear that an audible alarm having a typically loud alarm signal will be within audible range ( with respect to distance ) of at least one other of the alarms in the network . the alarm in the basement may not be within audible range of the alarm in the master bedroom , but it is certainly within audible range of the alarm in the kitchen . even if the alarm in the kitchen is not within audible range of the master bedroom , it is within audible range of the alarm in the living room . even if the alarm in the living room is not within audible range of the alarm in the bedroom , it is certainly within audible range of the alarm in the central hallway leading to the bedroom . finally , the alarm in the central hallway is within audible range of the alarm in the master bedroom . based even upon simple tests of sounding the alarm , one without any skill in the art can determine whether or not a particular alarm is safely within audible range of any other alarm . such a test would be conducted under the most adverse conditions , for example , with any intervening doors closed and any noise sources , apart from the alarm , activated . the ability to maintain the ease and simplicity of self - installation is a very important part of this invention . each alarm 10 according to this invention , and as shown in block diagram in fig2 comprises : an audible alarm , such as horn 12 , for producing an audible alarm signal having at least one predetermined or encoded identifiable characteristic ; means 14 for driving the audible alarm ; means 16 for detecting an abnormal condition ; means for detecting an audible alarm signal produced by another alarm ; and , triggering means 18 for enabling the alarm driving means in response to detection of either one of the abnormal condition and the audible alarm signal . the means for detecting an audible alarm signal produced by another alarm comprises a microphone or transducer 20 , a sound discriminator 22 attuned to at least one identifiable characteristic of the audible alarm signal , and means 24 for timing the duration of the at least one identifiable characteristic , a duration of two ( 2 ) to five ( 5 ) seconds being presently preferred . the alarm may further comprise means 26 for inhibiting production of the audible alarm signal for a predetermined time period , during which a number of activated alarms may be sequentially deactivated without an immediate automatic reactivation . in terms of a fire or smoke detector , the abnormal condition detector 16 , trigger 18 , alarm driver 14 and audible signaling device 12 are known in the art , and many variations thereof are incorporated into the many smoke detectors now available in the marketplace . one such circuit , which incorporates both ionization chamber and photoelectric detectors is disclosed in u . s . pat . no . 4 , 225 , 860 - conforti , the subject matter of which is incorporated herein by reference . in the dual input fire detector disclosed therein , it is necessary for the alarm to detect both visible and invisible products of combustion in order to sound the alarm . the outputs of the individual detectors form the inputs to a logical and gate , the output of which determines whether or not the audible alarm signal , in this case a horn , is to be activated . at this point in the circuit , namely at the signal indicating the presence of an abnormal condition , the means for detecting the audible alarm signal produced by another alarm may be connected or interjected , by means of a logical or gate or the like . such a circuit is illustrated in fig7 . a nand gate 30 has two inputs 32 and 34 . a high voltage or logic level &# 34 ; 1 &# 34 ; on line 32 indicates that the ionization chamber has detected predominantly invisible products of combustion . a high or logic level &# 34 ; 1 &# 34 ; on input line 34 indicates that the photoelectric cell has detected predominantly visible products of combustion . when both input lines 32 and 34 are high , indicating that a fire has been detected , the output line 36 , designated fire detected , goes low , a logic level &# 34 ; 0 &# 34 ;. in conventional fashion , signals which are &# 34 ; active low &# 34 ;, &# 34 ; low voltage true &# 34 ; or &# 34 ; high voltage false &# 34 ; at a particular place in the circuit are indicated by a line or &# 34 ; bar &# 34 ; over the signal name . line 36 forms one input to a nor gate 38 . nor gate 38 has a second input line 40 . input line 40 is connected to that signal which indicates that the audible alarm signal of another smoke detector has been detected , the signal being designated audible alarm signal detected . when either input 36 or 40 goes low , a logic level &# 34 ; 0 &# 34 ;, the output line 42 , designated detection , of nor gate 38 goes high , a logic level &# 34 ; 1 &# 34 ;, indicating that an alarm condition exists . depending upon the particular design chosen for the circuit , the logical functions could be performed by various positive rather than negative logic gates , or a mixture thereof . in a similar fashion , this invention could be incorporated into a combination fire and burglar alarm , as that shown in u . s . pat . no . 3 , 678 , 511 - benedict , the teachings of which are incorporated herein . however the connection is accomplished , it can be seen that the additional triggering mechanism interferes to a minimum extent with existing detector circuitry . irrespective of the abnormal condition which is to be detected , which need not necessarily be fire or smoke , a suitable alarm driver , including an audio signal generator is disclosed in u . s . pat . no . 4 , 079 , 271 - peil , the subject matter of which is also incorporated herein . those frequencies of sound most audible to persons are in the range of from 2 , 500 - 3 , 000 hertz ( hz ). most smoke detectors , for example , have audible alarm signals within that range . accordingly , the simplest of the presently preferred embodiments for the sound discriminator 22 is a narrow band - pass filter attuned to the chosen or existing operating frequency of the audible alarm signal . the band - pass filter should be as narrow as possible , in order to reduce the possibility of false alarms , and need only be as wide as the actual range of frequencies within which the audible alarm signal will operate . it is expected that as components are manufactured and selected only within certain tolerances , that no two audible alarm signals will be precisely alike , although that is possible . if the audio signal generator includes , for example , a resonant reed relay or a crystal oscillator , or the like , the frequencies can be very closely controlled . more particularly , the tolerances of components chosen , and the resulting capability of the detector to distinguish between an alarm condition and noise , will of course be a function of cost . at one end of the range of cost , an alarm signal generated by an inexpensive resonant reed relay could be detected using a similar resonant reed switch . at the other end of the range , a temperature compensated crystal oscillator signal could be counted down to the desired frequency and amplified , to be detected and compared to a clock signal generated by a similar oscillator in the receiving alarm unit . it is presently preferred that , for reasons of costs , the oscillator be composed of standard tolerance components ( e . g ., 5 % or 10 %), and that the frequency output be adjusted to a predetermined alarm frequency at the center of the band - pass of the detector , using a variable capacitor or potentiometer , when the unit is first built . in a unit employing the tuned frequency alarm signal and band - pass detector scheme , there are certain frequencies which should be avoided . inasmuch as many electrical appliances run at the power frequency , any multiple of 60 hz should be avoided . similarly , the usual frequencies of television horizontal oscillators and multiples thereof could cause generation of spurious alarm signals . in a somewhat more sophisticated version , the sound discriminator 22 may include a narrow band - pass filter 50 and a code detector 52 , as shown in fig3 . in the event that the audible alarm signal is not a continuous signal , but is a repetitive signal , in order to differentiate or prevent false alarms , it will be necessary not only to detect an audible alarm having the correct characteristic frequency , but also one which has the properly coded on - off characteristic . a suitable code detector 52 is illustrated in fig4 and comprises a pulse width detector 54 and a pulse repetition rate detector 56 . each decoder will be adjusted or tuned in accordance with the encoder which drives the audible alarm signaling device . each of these elements , the encoder , the narrow band - pass filter , the pulse width detector and the pulse repetition rate detector are well known to those skilled in the art , and need not be precisely illustrated herein . an operational difficulty has been anticipated in connection with audible alarms according to this invention . if the alarms are being tested , or if all of the alarms have been activated in response to a false alarm , it then becomes necessary to turn all of the alarms off . as a practical matter , it is nearly impossible to arrange turning off each of the alarm simultaneously . accordingly , as long as any alarm within audible range was still activated , any other alarm which was turned off would immediately thereafter be automatically reactivated . in order to preclude this possibility , means for inhibiting production of the audible alarm is provided . in the simplest of the preferred embodiments , the inhibit alarm may be a timer , electrical or mechanical , which can be set , for example , at 5 , 10 , or 15 minutes . alternatively , the length of time may be adjustable . electronically , the inhibit alarm might be a monostable multi - vibrator or oneshot , having a very long time - out . alternatively , it might be a simple mechanical countdown timer . the manner in which the inhibit alarm may be connected is also illustrated in fig7 . line 42 forms one input of a nand gate 60 . the other input line 62 is designated inhibit alarm . when line 62 is low , a logic level &# 34 ; 0 &# 34 ;, the means 26 for inhibiting the alarm have been activated , indicating no alarm should sound . when line 62 is high , a logic level &# 34 ; 1 &# 34 ;, the means 26 for inhibiting the alarm is inactive , and normal operation is in order . accordingly , when both inputs 60 and 62 go high , indicating the presence of an alarm condition and the absence of an inhibit alarm instruction , the output line 64 , designated enable alarm , goes low , a logic level &# 34 ; 0 &# 34 ;, whereby the audible alarm is sounded . if input line 62 is low , indicating the presence of an inhibit alarm instruction , output line 64 will be locked high , preventing operation of the audible alarm . as indicated in fig2 and 7 , it is presently preferred that the inhibit alarm means be connected to the trigger . as shown by the dotted lines in fig2 the inhibit alarm function may also be interjected elsewhere , for example in the timer 24 or in the line between the sound discriminator 22 and the timer 24 . if the user is willing to visit each alarm twice , to reactivate inhibited alarms , the function can be accomplished by an on - off switch . however , for a variety of reasons , the reactivation process may be interrupted , forgotten or only partially accomplished . this defeats the otherwise &# 34 ; fail - safe &# 34 ; nature of the of the alarm , and is not presently preferred . in the event of repetitive false alarms , or in the aftermath of a fire , it may be desirable to know which of the detectors was activated in response to the abnormal condition , as it will be an indication that the fire began in its vicinity or that a particular alarm unit is defective . an alternative embodiment of the trigger 18 in fig2 which would accomplish this is illustrated in fig5 . the outputs of the timer 24 and abnormal condition detector 16 would be inputs to an electromechanical marker 70 . in the event of false alarms , a light held by an electronic latch , such as a flip - flop , would be adequate , and if a liquid crystal display were utilized , the power consumption would not be unreasonable . however , a light system would not be suitable where a fire has finally put the alarm out of operation . in such an instance , assuming that destruction of the alarm was not utter and complete , a mechanical marker having a visible indication would be preferable . for example , a magnetic &# 34 ; flag &# 34 ; might be provided which has a brightly colored marking thereon , the position of which would be shifted , perhaps with respect to a number of adjacent windows . the movement of and the position of the &# 34 ; flag &# 34 ; would depend upon whether a signal was received first from the timer or first from the abnormal condition detector . the same signal which sets the mechanical &# 34 ; flag &# 34 ; can also be used as an input to the enable alarm driver circuitry 72 . resetting the mechanical &# 34 ; flag &# 34 ; can be adapted to initiate the inhibit timer . it is also contemplated that the principles of the invention can be incorporated into an auxiliary triggering mechanism to be added to existing self - contained audible alarm units . such a use is illustrated in fig6 . components of the existing alarm are shown in dotted box 74 . they include a smoke detector 76 , a trigger 18 , an alarm driver 14 and an audible alarm signaling device 12 . the auxiliary triggering mechanism includes a microphone or transducer 20 , a sound discriminator 22 , a timer 24 , an auxiliary trigger 78 and means for inhibiting production of the alarm 26 . the mechanism would be attached or interjected substantially as shown in fig7 and would be powered by the existing battery source . overall , this invention provides not only an improved audible alarm , but a simple means by which existing audible alarms may be formed into an operationally unified network which enhances operation for increased safety . in either embodiment , a minimum of additional power is required , as the existing audible alarm signaling devices are utilized as the communicating means between alarms in the system or network . finally , because the alarms are in fact so utilized as the communicating means , the overall alarm signal , in terms of absolute volume and ability to attract attention , is greatly multiplied . this invention represents a significant advance in audible alarm systems in general , and in smoke detector systems in particular , and has the capability of saving many more lives without significant additional costs . this invention may be embodied in other specific forms without departing from the spirit or essential attributes thereof , and accordingly , reference should be made to the appended claims , rather than the foregoing specification , as indicating the scope of the invention .