http://store.zips.com/proddetail.asp?partnum=02-640-125
here's a different model a bit cheaper. It's the lever model.
To lock:
-turn lever on
-hit brakes
Unlock:
-turn lever off
-and go
The neat thing here is you can cable operate the lever or hide it under the hood or back seat. But in responce to the brake pressure concerns, you simply turn the device on. Don't press the brake. So as soon as the theif backs the car up and hits the brake once, it locks. Theif can't go forward and is stuck doing burn outs in the parking lot, thief panics and runs.
What do you think? No constant pressure and it won't go far.