Tethercell lets you control mostly anything with Bluetooth (hands-on) @ The Verge.

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.