Detection of a specific sound

[alister]

On Tue, 03 Nov 2015 09:03:14 -0500, Dennis Lee Bieber wrote:

> On Tue, 3 Nov 2015 08:50:34 +0000 (UTC), alister
> <alister.nospam.ware at ntlworld.com> declaimed the following:
> 
>>Personally I would forget trying to analyse sound & see if there is any
>>way to get an input signal direct from the alarm (even if that is as
>>crude as taking a tap from the siren feed wires)
>>
>>This application sounds far to critical for anything else.
> 
> 	A direct line is what I'd recommend too -- but I'm going to be 
paranoid
> today:
> 
> 	If a fire did occur, and the inspectors find traces of wiring 
going
> into what was supposed to be a stand-alone detector there is a risk that
> it will be concluded that the detector had been tampered with and may
> not have been functional... And that could lead to all sorts of
> liability problems.
> 
> 	I don't know if anyone makes a model that falls between (common)
> stand-alone and full monitored (tied to burglar alarm system with a
> service provider responding to triggers). Something of a monitored type
> (hence designed to be wired to central panel) but without the outside
> monitoring agency.
> 
> 
> 	Barring that... if the detectors are all close in pitch, a PLL 
circuit
> fed from the microphone, using the "locked" signal to indicate when the
> alarm is chirping -- gives a simple on/off digital signal for the
> computer (the computer may be needed to ensure the chirps are at an
> expected rate and not stray whistles). Beyond that, FFT to look for
> spectral signature of chirps.

I would hope that most fire alarm systems (except domestic type smoke 
detectors) would have some relay outputs or telephone dialler options 
which would be legitimate locations to connect extra equipment.

The op probably needs to provide more information on the exact set-up 
intended.



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