1. Receiver for laser engine shutdown system.
High speed chases scare me.

Cop has laser, points it at car, engine stops.

No more high speed chases, no waiting for the drunk to notice the flashing lights.

(With appropriate security against non-cop lasers of course.)

2. DL reader. Swipe card to start car. Revoked license won't work - delivers shock instead. I hear MANY MANY MANY habitual traffic offenders, suspended/revoked drivers etc get pulled over when I listen to my scanner. (I'd rather they were roadside executed but I think that's too much to ask for.)

3. Cellphone noise source which jams cellphone service when the car is moving faster than 25 mph. Bonus for jammer that can deliver EMP to a text transmitting device.