Hi marv,firstly it's great to answer a post that has all the info required as we seldom do on here :),
Firstly a standard PIR is not suitable for that environment,take a look at one of the dual tech PIR's, look at fitting one of those.
Another thing check with your insurance comp that your garage contents insurance does really cover the cost of your tools.
Gud luck and as I said a dual tech PIR should sort it out,read the instructions with the dual tech and you will see why a standard PIR isn't suitable :)
e manno
February 2013