(Not so) Mysterious Black Box at Rachel Area 51 Gate

If anybody knows what this box is, I would appreciate any info. I was out at the Rachel gate to Area 51 and noticed this box attached to the gate. It is on their side of the fence. It is attached with regular plastic ties from any hardware store. The box had no wires going to or from it. It made no sound and it was facing any car or truck that entered the gate. It was on the right side of the gate. It was not there a few weeks ago. I am not really sure what it is. Any guesses?

Thanks to a poster on alt.area51 it appears to be a Dakota 3000 Wireless Motion Alert Driveway Alarm. It retails for about $159. Nothing but the finest to protect the worlds most famous secret base!