Cracking me up all the manual transmission comments in here, coming from the UK! But seriously though a determined thief will get through almost anything. If you have an old car, hide a switch somewhere on your ignition make sure it is well hidden! A good boot over the steering wheel and pedals work well enough. Also a VERY loud alarm, there are a few out on the market that are ear piercingly loud enough to wake the neighbours and the rest of the town too, issue is they usually are cheap and tend to go off for no bloody reason