My prefab garage was broken into last week. After failing at the back door they removed one of the roof panels.
It was a cheap pir alarm that alerted me to somthing going on.
I have now ground all of the bolt heads down on the roof and added another alarm to stop it happening again.
Multiple alarms which go off in the garage and the house are the way to go. I use the cheap Defender brand ones from CPC, never had any problems with spiders etc triggering them.
The more methods of securing and the more noise you can make the better.