12.7 Networked Smoke Detectors

Smoke detectors save lives and can help minimize property damage, but what happens when the alarm goes off when nobody is home? If you know what you’re doing, you can hook directly into the onboard electronics of the smoke detector to measure the voltage change when the alarm goes off, but doing so will probably void your detector’s warranty. It could also put the lives of those who depend on its life-saving functionality at risk if the device is improperly modified. Instead of soldering directly onto the smoke detector’s electronics, obtain an Electret microphone breakout board and use your Arduino and XBee skills to hook up, calibrate, and monitor the microphone input for the audio levels attained when the smoke detector’s alarm is sounding.[117] When an alarm is detected, have your XBee message-receiving PC relay you the message via an urgent email. You could even modify the Android server we used in Chapter 9, ​Android Door Lock​, to take a photo of the area being monitored by the smoke detector and attach it to the outbound message.

You could even link this alert to perform further actions, such as auto-dialing neighbors with a recorded message asking them to investigate the fire on your behalf and call you (just in case you never received the email). And if you’re really confident in your system’s sensing integrity, you could go so far as to auto-call the fire department if you don’t deactivate the alarm within a predetermined duration of time (though keep in mind that improper and/or nonemergency alerts could end up costing you, since many jurisdictions have penalties for false calls). Regardless of what enhancements you add, the fact remains that your smoke detector can extend its alert distance worldwide thanks to the Internet-enabled communication pathway you can devise for it.