I ordered three of these from a supplier in China for $3 or 98 cents a piece. I was going to order them from an American vendor for a slightly more, but I accidentally left them off my previous order, this was cheaper and I was in no rush to get them. I am going to use one of them with my LED lighting strip, so that the lights turn off automatically when I'm not in the room to save power. And I might also use them so they come on automatically in the evening -- but only if I am home. PIR are very easy to use, they are a self-contained module, that simply pulls a pin high for a period of time after a person is detected.