These smart smoke detectors are made out of old phones. Home surveillance company CleverLoop recycles Android smartphones into smoke detectors with the Smokey app (which is a free application, also for Android devices).
Smokey turns cell phones you aren't using anymore into remote smoke detectors with intelligent capabilities. To use, you simply ensure your functioning Android is plugged into a power source at home with the Smokey app on. The app can run even when the phone is in sleep mode, pulling from the phone's audio system. If it hears the fire alarm go off, it notifies the email attached to the account, so you will know if it's ringing even if you're not at home.
Smart smoke detectors like this one show not just a value for home safety, but also indicates the prevalence of smartphones.