Q: How do the automatic toilets and...

Q: How do the automatic toilets and faucets in bathrooms work?

A: A small laser in the sensor emits a microsecond burst of harmless infrared radiation every two to three seconds, according to Pete Jahrling of the Sloan Valve Co. When a person stands or sits in front of the sensor on a toilet or urinal, the light is reflected back to a sensor, arming the flushing mechanism controlled by a microprocessor. When the person leaves, the light is no longer reflected and the flush is triggered electronically. The device is powered by four AA batteries that are good for about three years, or 198,000 flushes, Jahrling said.

The faucets work in much the same manner, but the microprocessor in this case turns the water on when it detects a person’s presence.