Ask HN: How do you hang up a call on Android when the front camera is blocked?

It seems that if a piece of tape or a sticker is covering the front facing camera, the phone is unable to light the screen during a phone call to hang up. Bluetooth headsets make it possible to hang up, but what about without an external interface device? Is this because of the way the phone detects being pressed up against a face so that buttons don't get pressed? If so, can it be disabled?