There was a guy in my driveway last night...?

I would purchase a Chamberlain (or similar) Driveway Alert. It has a motion detector that goes outside and a base station inside that buzzes if someone comes up your driveway or sidewalk, etc. That way when alerted you can flip on lights or call 911 or scream or whatever, and 99 times out of 100 they'll just leave at that point.