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Both electret and piezo discs can produce over 100mV easily so you can almost feed them to a comparator directly. I very strongly advise you add some frequency filtering though or it will detect any ambient sounds too.  The advantage of piezo over electret is they are already resonant in the frequency range you are interested in and they need no power source so its easier to mount them remote from your electronics. It is quite likely the alarm sound itself comes from a piezo device.

I have seen applications using piezo discs to detect broken glass if windows are broken to gain entry to buildings because the sound of falling glass falls largely in the piezo bandwidth.

Brian.