I hear the most alarms go onto deaf ear replies but the fact is most of these alarms are tied into the ignition or starter.

My daily driver does not even have the siren installed. I basically have it for the convienience of keyless entry. The real benefit is when it's locked/armed, the ignition is disconnected. So even with the ignition switched punched out or even if the theif has my key. The alarm has disconnected the ignition system.

All you can really do is deter theft. As it was said, if they really want it, they will take it. The little blinking light in the windsheild will make most thieves look for an easier target.