Alarm system

An alarm system comprising:

• at least two alarm detecting devices, each alarm detecting device comprising:
• an alarm condition detecting circuit,
• a secondary alarm activation circuit, and
• an audible alarm output circuit including an audio oscillator and a speaker;
• said audible alarm output circuit being responsive to a detecting circuit control output generated by said alarm condition detecting circuit and to a secondary triggering output signal generated by said secondary alarm activation. circuit;
• said secondary alarm activation circuit including:
• a microphone having a microphone output signal,
• an amplifier circuit in connection with said microphone output signal and generating an amplified output signal,
• a tunable filter circuit having a filter input in connection with said amplifier output signal, said tunable filter circuit generating a filtered output signal in a first predetermined frequency range, said tunable filter circuit including a tuning mechanism tunable by a user to set a desired said first frequency range;
• a filter signal integrator having an integrator input in connection with said filtered output signal for integrating said filtered signal output and generating an integrated output signal;
• a reference signal generator having a reference signal output;
• a comparator circuit having a reference signal input in connection with said reference signal output and a compared signal input in connection with said integrated output signal, and generating said secondary alarm triggering output signal when said compared signal input exceeds said reference signal input.