Re: A home Project
There is one problem with PIR sensors that just came to mind. These sensors detect movement. The problem here is if somebody is sitting still, perhaps reading a book. You have to make sure that this isn't interpreted as the room being empty.
I found this product from Leviton, but the way they get around this non-movement issue is simply to use a settable timer to turn off the light after X minutes of no movement is detected. That's a bit of a kludge, IMHO. Imagine how annoying it would be if while reading a book, every 15 minutes the light goes off.
**broken link removed**
There must be a better way. That link still has some interesting PDF files describing how this switch works.
A quick Google search of the term "occupancy sensor" showed some promising links.