Sam, I've been wondering about the comments on animals. It makes sense that a deer would turn the lights on. If it is supposed to be up for trespassers.
The problem with the one next door is that the wind moves tree branches about 20 yards away and that turns the lights on. I would imagine that any tall plants would do the same. That would seriously limit some people's use for the lights.
That yard is completely devoid of any other tall plants but the trees are enough. Now that I think of it, the remaining 2 arborvitae were taken out about the time the lights were put up.
off topic: (I asked about those bushes but didn't really get an answer. The trees may be a sensitive issue because the 1st ex-husband claimed that the property line included those 2 trees. There is an ancient metal post that suggests that one is on one side and the other on the other side of the property line. I built a fence 15 years ago that he first claimed was 2" on his side then said was 2' ..! He, however, is long, lloong gone and been replaced twice. One of these days, those trees have to go but it shouldn't be motion detection that determines when!)
Steve