I like this group, most of you fellas are pro's. But for an amateur project I took a standard off-the
-shelf Smoke Alarm and found it only takes IMohm to ground (to negative) the test button to activate the alarm.
So I attenuated the resistor going to the pzieo to make it quiet, then I fed the output of the alarm into a circuit that shuts off the SA test circuit ie feedback attenuation, and as a result it sounds like a pleasant bird chirping, until it powers down - I used a cap to power it up.
Why did I post that? Well sometimes you want a fast and cheap audio annuciator, with a built in SA. Regards Ken