People from Ausmini Mk 1 will remember my input into this topic. If you didnt read those topics, lets just say I have much experience....
Forget piezzo screamers. They might be good in new cars cos you can hide em in the mass of wires, but in minis you cant hide em very well. All you have to do is find it, and pull the wires out to stop the noise. Waste of money. Trust me.
Whats more, a good thief

can recognise an alarm by the flashing pattern of the light on the dash (LED), and the sound the alarm makes when it arms/disarms. If they recognise the alarm, chances are they know how to bypass it. I know
I can.....
Basically, a mini is easy to break into. Even if they
dont take the whole car, they will take things inside it (eg: gear knob, clothes, cd's, engine parts....). To
get in sometimes means to break things, either a lock or a window, so if you dont want
any damage to the car, i suggest an alarm with microwave sensors - something that will detect movement
around the car which then sets off the pre-alarm warning.
Thieves dont like noise starting before they get in...
p.s: Who needs a towtruck??? A mini can be stolen using another mini and a towrope.... i've seen it done...
I didnt mean to scare people with this, but it IS reality....