I have a Dakota Alert, which is just motion activated similar to the door sensor at a grocery store. It works. I get a lot of false alarms though. Cats, rabbits, any wild life that walks by sets it off. Its acceptable for my driveway and house.
If I had a large driveway, I would not use a motion alert system. I would use one of the ones that detect magnetic fields/metal, so that small animals don't set it off.