That facemask detection at entrance to Tesco
At my local Lotus supermarket, they have a table with a facemask detection system. It is installed in such a way that a small children or a tall adult are out of the way of the camera (anyone not in the 5 to 6 foot height I'd say). And of course, they need one staff to man the equipment, so the real benefit is negative (same number of staff, but added cost of technology).
Local is rural Thailand, I cannot say for other branches, I have only been to that one in the past few weeks.
On the part about privacy, I don't really consider it a breach of my privacy if a screen displays a message saying that I do not wear a mask while other punters around me could see by themselves that I do go uncovered.