I know there are motion sensors which detect movement and can turn on
a light fixture. What I was wondering is there a way to do this inside
a house? I would need one that would detect a person walking _into_
the room so the light would cut on several feet before a person enters
the room.

Is there a relatively cheap and easy way to do this?
Perhaps I might want to do only one room to see how it would work out?

thanks,