Wireless Tag Weather protector
This is a waterproof box that just fits the http://WirelessTag.net motion sensor tags.
I make it of ABS and use acetone vapor for half an hour to make it shiny and waterproof.
Screw it to wood with #6 brass woodscrews, with the closed end upward, and slide the tag up into the box.
There's a detent to hold it in place until you pry it out using a sharp tool (like the sharp screwdriver you'll need to open the tag to replace its battery).