Be very careful where you take it. An alarm is only ever as good as the person who installs it. A badly fitted alarm is an absolutely miserable thing, trust me, and a lot of the bigger companies vary massively depending on who does the work.
I've heard lots of good things about Dennis at Alarms4U, a few current and ex Max staffers have used him to fit alarms (and repair shonky work done by other, supposedly reputable, places). He's local enough to come out and do cars around the Peterborough area.
alarms4u.co.uk