What is the name of the function on the iPad - closing the cover of the cover?

Question

iPad

I bought a cover for an iPad and noticed an accidentally convenient function in it, when you close the cover, it automatically locks. How does is called?
PS and how is it implemented, is there some kind of sensor there?

Answer 1

1. And when you open it, it unlocks :)
2. It's not called in any way:
3. there is a reed switch in the iPad case