An immobiliser is a requirement on all new vehicles developed since 1998 and stops the vehicle from currently being removed without the appropriate important or fob. This is probably going to generally be why you at the moment are currently being asked to put in a Thatcham approved tracking machine, https://medium.com/@trackerfit11/why-choosing-a-thatcham-tracker-strengthens-vehicle-security-6b79d8a9c256