My last house was built in 1947. It has an unusual low voltage sytem in which relays are actuated by a low voltage circuit. Its kind of neat, becaue the relay is placed near the load, and doorbell wire is from from the switch. Therefore, you can have a switch activating a light or device 10 feet away or 100 feet away without having to run full current handling cable. The wall switches are momentary contact rockers. The parts are rather hard to find, and very few electricians have ever even seems these systems.