I'm thinking about automating the lighting system in my bathroom. I made up a 5V and 12V power supply from a transformer I salvaged from some old circuits. I need to turn on the lights when I'm going inside if the ambient light is below a certain limit and I think I can use a LDR as a sensor here and turn it off when I'm walking out side.
Why I posted this here is I need to know a method which consumes less power that can detect movement across a door. So I can use a relay to turn the lights on and off. Thanks :)
Edit: I was thinking about using a sonar sensor and a microcontroller but that is a little complicated right?