Our new best friend: the TP-Link 70xN series wireless router, running OpenWRT. The LED is what drives the transistor, which in turn switches the 8V power supply to drive the door lock. The other dangling transistor is the good ol’ 7805 for powering the router.
The router is running a small LUA webserver, which listens on http://door.xinchejian.com:8080/ and serves a web page where you can enter the pincode for the machine room. When the code is correct, the LED is turned off, and current stops flowing through the door lock, which opens the lock. (The lock needs power to keep the door closed.)
