hand crank. But seriously, build the contactless key in such a way that it must be inserted and turned like a traditional key, and the battery will last a very,

hand crank. But seriously, build the contactless key in such a way that it must be inserted and turned like a traditional key, and the battery will last a very, very long time[0] since you're not using it to mechanically retract the deadbolt or operate an electronic strike. Then build an LED to warn when the battery is getting low, giving you months to replace it. Don't use [0] though, or you'll have a mini-USB port sitting behind a rubber flap on the non-secure side of your door. Oh wait, you don't even need that to bypass it, just a paperclip and a few seconds (there was a youtube video of this that appears to be taken down, I tried it on my own apartment). [0]http://www.kabamultihousing.com/Products-Solutions/Multihousing-Solutions/RFID/329314/insync-locks.html http://www.kabamultihousing.com/Products-Solutions/Multihous...