Tag, I had one of my previous Camaro's broken into. :(
Afterwards, I looked into getting an alarm, but after speaking with several people, including the police officer who took the report, it was suggested I save some money just go with the factory alarm. Reason being, if the thieves want your car bad enough, they'll get it no matter what alarm you install. The officer told me of stories where the thieves would drag cars onto a flatbed, etc.
So, per his suggestion, I stopped at a local automotive store and purchased 'The Club' (which I know is easily removed in seconds), as well as "This car is alarmed ....." decals which I placed on the side windows.
The officers reasoning being that you want to make your car appear
to be more difficult for a thief to steal. If they walk up and see your car with the "security devices" versus one next to it without any, the thief may choose the other car. From his experiences, theres not an alarm out there to stop them.
If I were to purchase any aftermarket system, it would be 'Lo Jack'. I may not be able to stop a thief, but there'll be a better chance the car is located before too much damage is done.
A simple solution though, I never take the SS anywhere where it'll be parked for more than 15 minutes.