Q. The last time I used the facilities at our local airport, I noticed that the toilets (or urinals) flushed automatically when I moved away. OK, I figured they must be ultrasonic or infrared. The question that really puzzled me was "How do power the devices?" There are no wires to the sensor unit, and I can't believe that someone has to come around and change batteries regularly. Is it possible that these devices are powered off of miniature generators taking power from the moving water stream? Or do they hide the wires inside the plumbing? If you're talking about the type that has a black plastic dome over the flush valve regulator (the chrome piece that usually has a bat handle sticking out), they are powered by 4 AA alkaline cells. Service life is over 50,000 flushes. The design is a marvel of energy efficiency. Active infrared sensing (modulated LEDs), very low duty factor, and magnetic latching pilot solenoid valve. If you do a web patent database search on 'flush valve sensor' you can learn more.