7. A device that automatically disables any cell phone in any car within 50 car 
    lengths of me and heading in my direction.

I think this device would have the opposite effect that you hope for. I wonder how many days you would last with it?

Multiply the number of talker_drivers you meet with the probability that one of them can't handle the extra distraction of driving and banging on his cell phone, trying to reconnect his call that you jammed. Imagine on a busy commute, this happening every two or three seconds.

Actually, this could be a murder mystery plot, on par with cutting the brake lines. Hide a jammer in somebody's car, and wait for the inevitable result.