Reader Christian brought this to my attention.. (http://www.simpleiothings.com/10-diy-wifi-smoke-alarm-notifier-roost-nest-alternative-full-tutorial/)
The guy uses a NodeMCU, a USB wall power supply and audio sensor (microphone) to catch the audible alarm and start a WiFi alert via IFTTT. The smoke alarm unit stays unaltered and you never have to think about running out of power during broadcasting. It may even work with multiple smoke detectors in different rooms. It sounds dirt easy to set up. This looks like a perfect simple solution when you’re not at home. Ok so any ESP board would do – the NodeMcu is just a simple option – and of course given the price at the likes of Banggood not a bad one.
At the cottage here which is rented out in summer when we’re off to the sun, we do of course have fire alarms – and BOY are they loud – but if there is no-one in…. yup – a good idea. It just so happens I have one of those £2 audio sensing boards and as soon as I finish writing this blog I’m adding it to the living room temperature sensor! Of course all I really need to do is pick up that loud noise and get it into Node-Red which can then send me an email! The beauty of this is – no messing with the existing alarms.
Next step would be to send a sound sample (may require an additional microphone) or picture (OV7670 camera as seen working with Arduino).