I thought this was normally done by requiring the guard to regularly scan special tags physically located around the premises being guarded (or previously, by k

I thought this was normally done by requiring the guard to regularly scan special tags physically located around the premises being guarded (or previously, by keeping "watch clocks" wound). https://en.wikipedia.org/wiki/Guard_tour_patrol_system https://en.wikipedia.org/wiki/Guard_tour_patrol_system