We got a $15 driveway alarm from Harbor Freight. I think it is Western Safety brand. I hung it on the post by the entrance, about 75 yards from the house. The alarm is hung in the kitchen. Now whenever a car drives in, we get two beeps. It only had one hole for mounting and the wind blew it on the post, and that would make it go off all the time, so we wired it tight to the post. The first night at about 2 it began beeping lots of times. We got up and shined the spotlight out and found a herd of mule deer headed for the strawberries. Now we chase them off every night when it beeps. Sometimes a magpie playing around a puddle will set it off, and sometimes swallows cruising by will beep it, but usually it is quiet. And it even tells us when the people drive thru the neighbor gate, which is probably another 50 yards away. Luckily they don't use it much.