Project enclosure for the Velleman Metal Detector Kit, commonly available at Radio Shack.
Clip the PCB into the bottom of the case. (You may need to bend the corners out a bit, but it should snap right in.) The 9V battery fits below the circuit board. There are four little hooks around the perimeter that might print well if you send it off, but I haven't had success with them on a reprap, so I just hold it together with tape.
Here's a link the the Velleman kit this was made for: http://www.vellemanusa.com/products/view/?country=us&lang=enu&id=350591