Fitted a Hawk alarm. (http://hawkcaralarm.com/). Thought I would do it myself, then decided to get professional help. I felt that I didn't want to mess up the electrical system...So, although I knew where the wires should go I thought I do it the safe way.

The alarm was very good quality. Even the guy that installed it didn't believe me on the price. For the money (GBP £35 shipped) it was a steal. It also included a tilt sensor which was not functioning. The seller said he would replace that sensor immediately. Will see.

The alarm works fine to date and had no false alarms. Scares those cats away too :D

UPDATE: The tilt sensor was functioning normally. The instructions included a typo...it should be connected to permanent ground. The instructions indicated non-permanent ground. So issue has been resolved. I am not happy with the tilt sensor though, it only causes false alarms and does not offer any additional protection.

I am just saying if you are interested in this alarm, go for the one without the tilt sensor. Still a good product, just don't pay for the tilt sensor.