Fitting an intruder alarm is a great idea however I wouldn't recommend it as a project for a DIY beginner. Far better to get in an Alarm specialist in.

Having said that there are now available a number of wireless alarm systems which are much easier to install which you may like to tackle yourself.

For easy to fit wireless systems checkout:

www.alertelectrical.com

www.quicksafe.co.uk

www.home-monitoring-systems.co.uk