This sounds fairly easy to defeat...just put it inside of another solid object. A Keltec could probably fit into something that looks like a large PDA, personal CD player, or SLR. Apparently, mm-wave is deflected when it hits something like that, which is what makes it work in the first place. You could get one of those huge old Canons that use film, hollow it out, and make a mm-proof external carry holster for about $50.

As usual, "another tool for law enforcement" would solve nothing.