Everything is getting “smarter”, how many things are now “connected”? You can add the simple 9 volt battery to the list of connected devices. The Roost is a wifi connected battery that is the same form factor as a 9 volt battery, it connects to your wifi router in your home to allow it to send out notifications. It has the ability to let you know when the battery is low and also when the smoke detector is going off. Since this device is simply able to be inserted in your existing smoke alarms I am thinking that it must be looking for a current draw change when the smoke alarm is in alarm (making noise).