Motion detectors don't work beyond 2 feet

Does anybody’s motion detector work? It doesn’t work for me unless I walk right in front of it within 2 feet. I’m 5’2’’ and even if I walk directly beneath it, it doesn’t sense. I could have 20 motion detectors on a wall and still an intruder would be able to get past it because they don’t seem to sense anything beyond 2 feet, and not even motion 3 inches below.