Switch any of the three switches off or on, the LEDs will change "off" or "on" depending on the opposite of the current setting. It's a 3-bit "X-OR" gates, or a 3-bit parity circuit. Let's say you cross a hall once, but you are far from the switch on the other side and you are done with the lights, the next switch will turn it back "off" or back "on" depending on what you left it as, this one is a three way switch so you can use it in a three "y" intersection hall. You can also use it in a three entry way room.
