I fit the RAC Trackstar Plus

Be warned though - some thieves are now using Jammers to stop Trackers from working. They are not common but it does happen.
Also check out the anti hook & cane device -
www.newministuff.com look at the security section.
Another bit of bad news I heard this weekend. - Thieves have now obtained computer equipment that can disable modern factory immobilisers

It is reported that David Beckham has just had one of his cars stolen this way