X-10 (www.x10.com) has motion detectors for around $25 (they used to
have an indoor-only one for less but I don't see it in their current
list), and you can buy things that either replace your light switches
or screw in between your light bulb and the socket. And you'll need a
receiver.

If you're not in a rush, they're always running some sort of sale, so
you can wait until the parts you want are on sale. Not a lot of reason
to pay their retail prices.

You'll have to do a bit of reading to understand how their stuff works,
but I've found it a lot of fun and very helpful around the house. I
can turn on and off lights from anywhere in the house by remote
control, or turn them all on at once. When I go out the back door at
night the under-deck lights also come on automatically. My air filter
is on a timer to go on at the times I'm normally not home. And instead
of an alarm clock my stereo gently wakes me up in the morning.

Shaun Eli
www.BrainChampagne.com
Brain Champagne: Clever Comedy for Smart Minds (sm)
Now with a comedy video on the website!