Brad Fitzpatrick has hacked his HTC G1 Android smartphone to use it as a secure remote which can open his home's garage door as he gets close to it. Using Wi-Fi, the mobile phone automatically fires up an HTTP request to his home server as soon as it's near enough, which triggers the opening as well as other functions in the house.
The system starts with the Wi-Fi scanner function of the Android: His programs calls the WifiLock service from the system-wide WifiManager, which fires requests every two seconds looking for the house wireless network. This doesn't happen all the time, so the waste of battery is less than what you think. The software only activates when he presses a button which basically tells the program that he's going back home.
I know. If it requires a click and it consumes battery life, even if only a little, what's the point? Why not get a normal remote? Probably because he uses a motorbike and he doesn't want to stop to find the remote, click, and then keep on going, specially in winter.