Here's a teardown: [guide|98975] most likely it is the ambient light sensor, the same component that controls auto brightness and turns off the display when you put the phone up to your ear. So when the cover closes, it becomes dark and that turns off the display. Seems about right.
+
+
=== Update (11/30/2017) ===
+
+
Ah. Found this in apple support:
+
+
"When the folio case is closed is there a magnet or something along the lines of a magnet which keeps the case closed?
+
+
Asked by kris I from hull on Sep 14, 2017
+
+
Best Answer:
+
+
There is a magnet in the cover, but its utility is to wake the phone on opening the cover, not to keep the cover clamped shut. So if you drop the phone in this case, expect the cover to open."
Here's a teardown: [guide|98975] most likely it is the ambient light sensor, the same component that controls auto brightness and turns off the display when you put the phone up to your ear. So when the cover closes, it becomes dark and that turns off the display. Seems about right.