@tmaster
Actually, the KY-038 works exactly what I want (except for the power consumption). I also have ones that are connect to mains power, and the false alarms are rare. Also, I have the Arduino programmed to sleep some time after detecting a sound and sending a message. In the case of a real alarm, it will keep sending regularly, which would make it obvious. The "batteries just end in a few months" is what I'm asking about - avoiding the .4ma used by the LM393. I'm hoping I can replace it with the LMV393, but I'm not sure if it will work.
Regarding the "you think you are safe", Mysensors has heartbeats, and battery percentage reporting to deal with all that.