The 1/2 Mile Driveway Alarm from Hammacher is exactly what the name suggests. It will alert homeowners about approaching vehicles in your driveway even when the vehicle is as far as half a mile away. Of course, you would need a driveway that stretches that long, and not all of us have country manors surrounded by extensive grounds. But the point is that you can attach the alarm sensor to a postbox or sign post at the end of the driveway, and the motion detecting sensor sends a wireless signal to the monitor inside the house whenever it detects people and vehicles passing through. You can set an exit delay so that it doesn’t start clanging when you go out. The monitor at home can be plugged into a wall outlet, and the sensor works on a single battery.