Turn an old-style but still functional smoke detector into a Wi-Fi-connected sensor with the Roost smart battery.
Replace your 9-volt battery with this $40 device, which adds a Wi-Fi chip and two lithium cells. It gives you power for the detector for up to five years.
The chip connects to your home’s Wi-Fi network and sends an alert, via smartphone app, when an alarm sounds or when the battery needs to be replaced. Available in June; preorder at smartroost.net.