Sometimes a wall switch needs to be kept in a “normally on” or “normally off” position. For example, outdoor security lighting with a motion detector should be kept “on” all the time.
This simple, small device is easily installed using the existing screw from the wall plate. I call it a “reminder” because it’s very easily rotated away from the switch if desired so the switch can be moved to its other position; it does not really “lock” the switch in any permanent way, but “reminds” people not to change the switch unintentionally.