Nest Protect

Nest Protect tells Homey the second it senses smoke, carbon monoxide or heat, instead of Homey finding out at the next poll. Every alarm also reports its battery, whether it has been taken off its base, and a manual test you can use to check the whole chain works without setting anything alight. Because smoke alarms are silent for months at a time, the app can also tell you when it loses contact with Nest, so a broken connection stops looking exactly like a quiet house. Google's own smart home API has never covered Nest Protect, so this app signs in the way the Nest app itself does: you copy two values from a signed-in browser session once, and the app settings walk you through exactly where to find them. Your Protects detect, sound and interconnect entirely on their own, whether or not Homey is running, so treat this as notification and automation on top of that, never as a replacement for the alarms themselves.