Just installed a new porch light fixture for my mother-in-law. Found these great light bulbs that have an electric eye. Just keep the light switch on and the bulb turns on at dusk and off at dawn!
Click on image for link.
So when I was working on this post I found radar bulbs! This one says it can sense movement through walls! I wondered with all the skeletons that turn on automatically for Halloween when more practical applications might arise (with the monsters)!