Cat detector
How dark are a cat’s stripes?
We have a night-light near our apartment door which is itself light-sensitive, which is to say, it has a little eye on the front which measures ambient light nearby. If it’s daytime, or the lights are on in that room, it stays off. If it’s dark nearby (that is, neither of those conditions are true,) it lights up.
Like most outlets, the light is at approximately cat height. When Iz walks by, the light flickers on.