I have a trackstar fitted to my van.
Brilliant. Once in a while they ring you up and tell you where your van is eg, post code and which house number you are parked outside.
If i'm not mistaken you have to have an immobiliser fitted before you can fit either systems.
Sits dormant until alarm is triggered or the van is moved without the engine running or someone tries to start the van without the key.
Mine has been fine, even when i took the battery out and a week later put a new one in, no problems.
When i broke down and the AA piggy backed me home, i didn't think about the tracker. Within 3 minutes of being on the back of the AA wagon and moving they had notified the police and rung me. They advised me my van was moving on the M62, East bound between junction 21 and 20.
After goiong through security checks, they politely asked me to let them know in future - oops.