I had a Viper 2 way security system installed when I had remote start added. Entire package was around $700. The tech can set the sensitivity of the motion sensor. I recently backed into a parking and left my H2. When I was a few blocks away, my remote signaled that motion was detected. When I got back to my H2, some dork cut too close when they tried to pull into the parking stall next to me. Fortunately, he only grazed my front brushgard and I couldn't even tell he hit it. He did manage to crunch the front quarter panel of his F150. You can find info on the Viper here:
http://www.directed.com/security/vip..._responder.asp