Why spend $100 for a new smoke detector that will alert your smart phone when it needs a new battery? The people behind Roost say just replace the dumb battery with their intelligent battery, which includes processing power with various wireless sensors to communicate the status of the smoke detector. For $35, their smart battery, which is in the form of a 9 volt battery, adds intelligence to the dumbest of smoke detectors. They have even made it modular, so in 5 years when a new battery is needed, only that portion of the device will need replacing at an estimated cost of $10.