We have a fairly long hedge lined driveway and it is impossible to see people coming and going from the inside of our house. We also have no windows on the side of the house facing the driveway (not a well thought out house design). We bought this system from a friend who sells alarm systems. He assured us that it was professional grade and a high quality system. He even gave us his cost of $100. The only problem was that we had to install it ourselves.
It took my husband a few attempts to get the sensor angled just right but now that it's in place it works most of the time. There are occasions where it will go off and nobody is there. We assume it was birds or maybe the wind blowing around the hedges. There are also rare occasions where it will miss a vehicle, mostly my husbands large box truck. I'd say it works correctly over 90% of the time and that does help give us piece of mind. It dings everytime someone walks down the driveway also. It scans in a fan pattern, not just a flat beam so that it catches more movement than some other systems.
The receptor "dinger" is kept in our dining room and can be plugged in or ran off of batteries. The dinger is loud enough to be heard throughout the house. The sensor in our driveway is visible and we hope that in itself would be a deterrant to anyone thinking about burglarizing our home. It was money well spent in our book.