Exactlty the system I have been looking into today.
On my 2002 and my 2005 I had Boomerang II installed. That system uses a transponder to detect whenever the car is moved without the transponder in the car. I trusted that system for years and I still do.
Couple of years ago, Quebec company Boomerang was bought by American company LoJack. It sells for 900$ installed with no annual fees for 7 years. That makes it more affordable then the Boomerang II ever was.
I like it. Do you or anybody you know have it ?