ORIGINAL: dereksharpuk
Well I have now read thoroughly my Cobra VTS service booklet and owners manual and nowhere does it say they could immobilise the vehicle. If you come to think of it, that would be very dangerous. The OPC that told you that must be pulling your leg!
Not sure about Cobra, but iMob trackers do have an immobilisation option. But safe because they only immobilise a non-moving vehicle (system checks the GPS for vehicle speed, or ignition off on cheaper versions). It lights up the hazards at the same time.