Yes, but those only detect movement[1]. They cannot differentiate between a motionless person and the rest of the room. Hence my point about the problem with motion detectors in a house given that most people often spend periods of time largely motionless.
There is a workaround to this problem, but it requires adding a networked "intelligence" to the detectors. You'd a detector at every entrance and every exit of every room. Then you'd need to network them up to a server (which defeats the advantage of motion sensors over FIND) and that would log the movement in and out of each room, incrementing the occupancy of the room as it goes along to ensure that lights are not deactivated when two people are in the room but only one exits. By the time you've installed dozens of sensors across the house, networked them, and installed a server, you might as well have just gone with FIND. Not only does FIND require less hardware, it can identify the specific individuals and isn't triggered by family pets (I certainly don't want my cats turning lights on during the night!)
So while you are right that other, simpler, technologies have been around for years, they're simply not good enough for the average home (it still remains to be seen if FIND is, but it's definitely better than motion sensors)
There is a workaround to this problem, but it requires adding a networked "intelligence" to the detectors. You'd a detector at every entrance and every exit of every room. Then you'd need to network them up to a server (which defeats the advantage of motion sensors over FIND) and that would log the movement in and out of each room, incrementing the occupancy of the room as it goes along to ensure that lights are not deactivated when two people are in the room but only one exits. By the time you've installed dozens of sensors across the house, networked them, and installed a server, you might as well have just gone with FIND. Not only does FIND require less hardware, it can identify the specific individuals and isn't triggered by family pets (I certainly don't want my cats turning lights on during the night!)
So while you are right that other, simpler, technologies have been around for years, they're simply not good enough for the average home (it still remains to be seen if FIND is, but it's definitely better than motion sensors)
[1] As per the article you cited, details about how the detection on works for objects in motion: https://en.wikipedia.org/wiki/Passive_infrared_sensor#Operat...