The "internet of things" is great, in theory — the problem is that you need new connected stuff to replace your old unconnected stuff. Tethercell is trying to fix that: it's basically a plastic sleeve that converts an AAA battery into an AA, grafting on Bluetooth 4.0 support that lets you control the flow of power with a smartphone. It can also send you alerts when you're low on power, set on-off timers, and so on. In theory, it should work with any of the millions of gadgets out there that run on AA cells.
But there's a problem: it's not real yet. Bluetooth SIG — the body responsible for Bluetooth certification — was showing off the unit at its booth this evening, but the Indiegogo project to help fund it won't kick off until next week (pricing tiers aren't yet being disclosed). Another concern is power draw; running a Bluetooth 4.0 radio, no matter how low-energy, will have an impact on how long a battery lasts in a device. The engineers behind the project believe that they'll be able to get somewhere between six and twelve months of life on a single AAA battery, but the actual runtime obviously depends on the device that you use it in.
Is it practical? Maybe, if the final product is cheap enough and the company can pull it off. Imagine turning off all of a child's toys when it's bedtime — you're going to be hard-pressed to find Bluetooth Low Energy-compatible Furbys on store shelves right now.