I looked into having a tracker fitted last year for insurance purposes. From the top of my head it worked out at £189 fitted and £11.99 per month for a service that could be activated 24/7 365 days a year. It got me a whopping £300 off my insurance quote so I didn't bother.
If my car was stolen I doubt I'd really want it back, my excess is £200 and iv got my maximum no claims bonus protected. I'd like to think a tracker might lead to prosecution of the person who stole my car but in reality it would either never be seen again or found parked up in a side street needing 2 new tyres, fuel, stinking of weed and scratched to fook.
Can't beat the old hidden switch to the fuel pump trick IMO :)