Radar Gun Stops RPGs explains how simple off-the-shelf technology can solve a serious problem:
Whoever thought a radar gun and an airbag could provide protection from RPGs. The U.S. has spent billions of dollars in the last few years, to make unarmored vehicles less vulnerable to RPGs and roadside bombs. All that money has made it possible for a lot of odd ideas to be tested. One of these is TRAPS (Tactical RPG Airbag Protection System). This uses a modified car airbag, the radar technology found in police radar guns, and some pretty basic control software. Once TRAPS is turned on, it’s radar constantly scans for any object fitting the size and speed profile of an incoming RPG warhead. If one is detected, the airbag deploys, and sets off the RPG warhead a safe distance from the vehicle. A system capable of protecting a small military vehicle, like a hummer, would weigh about 125 pounds, run off the vehicle power supply and cost about $10,000.