In an installation for determining the number of persons inside a monitored room or so-called pass-through, a sensor field is generated by IR-sensors. An evaluation unit uses as discriminating criterion the detection of moving bodies and generates for an entrance control unit a signal, allowing or barring...http://www.google.ca/patents/US4847485?utm_source=gb-gplus-sharePatent US4847485 - Arrangement for determining the number of persons and a direction within a space to be monitored or a pass-through
