While yes, these devices are cool and I use them in a couple of projects (mostly centered around home automation), I think there is no good way to count people that way (other than placing them above ingress and egress points).
I think the original use case is not to know whether a dining hall is occupied at all but about how occupied it is (and if he should go to lunch now or wait another 20 minutes).
I think the original use case is not to know whether a dining hall is occupied at all but about how occupied it is (and if he should go to lunch now or wait another 20 minutes).