Internet-Connected Battery Could Bring Smoke Alarms Online A startup has come up with a simple way to make smoke and carbon-monoxide detectors more useful: a nine-volt battery with built-in Wi-Fi. The battery can alert you on your smartphone if the alarm goes off or the battery itself is about to die.Roost the Sunnyvale California-based company behind the battery plans to sell the batteries starting next year for $25 to $35.    We were approaching the Internet-of-things space not from a perspective of   ��How can we build a whizzy new device that does something?    but   ��What information do you have in the house that   s useful to you that you   d like access to when you   re not home?       says cofounder and chief technology officer James Blackwell.The idea could reach beyond alarms. Roost has its sights set on other devices battery-powered and not that are currently excluded from the growing throng of connected gadgets.Roost   s first batteries which are lithium-based and meant to last for more than five years contain a Wi-Fi chip and sensors for audio detection and voltage monitoring. To get one working with a smoke alarm you   d set it up with a forthcoming Roost smartphone app. Using the app you can give a battery a name (like     living room   or     kids    bedroom  ) and connect it to your home Wi-Fi and then insert it in the battery compartment of the alarm.Right now Roost has a working prototype in a plastic box about the size of an external hard drive; Blackwell expects a battery-sized version to be ready in the spring.Roost plans to go beyond the nine-volt battery in the future  ��Blackwell says the company is thinking about AA batteries since they   re commonly used in toys and remote controls. He   s also thinking about adding other sensors such as an accelerometer or thermometer to the battery.