relay lights
The lights that must be turned on and off in a sequential order so you can safely make it from one area of the house to another when it is dark.
I came in through the back door and had to set relay lights in the kitchen, the dining room and finally my room. I then had to turn the relay lights off in that order: the back door light, the kitchen light, and then the dining room light so I could safely make it to my room without tripping over chairs or hitting counter tops or walls.