2016 rear hatch open sensor faulty?

What device, sensor or momentary switch tells my Prius the hatch is open?
Today I opened the rear hatch which, as always, unlocked the car. However, the car locked itself automatically the same way it does if you unlock but don’t open a door. I checked further and found Prius can be locked with key or sensors even when hatch is open. Also, hatch open light on dash does not light up.
If I can find the switch or sensor, I can test or replace it.