My garage is separate from the house by about 20m. There is currently
a bit of a worry about security and I have rigged up a burglar alarm.

It then struck me that it would be a bonus if I could link a smoke
alarm into that too. Electronics is my training so I don't have any
problems in that area, but I've dismantled the smoke alarm (ie got it
out of the plastic !) and am puzzled to see that the piezo sounder has
3 leads - why ?.

The IC is under the sensor cover - would anyone know if that is likely
to have a dc output rather than the switching one for the sounder ?

Thanks
Rob