Abstract: Occupancy detection is an increasingly important part of building control logic, as new systems and control logic greatly benefit from human-in-the-loop sensing. Current approaches such as CO2 monitoring, acoustic detection, and PIR based motion detection are limited in scope, as these variables are a proxy for occupancy, and at best can be roughly correlated to occupancy, and cannot reliably provide a count of the number of occupants. The disclosed sensor uses thermal information that is continually being emitted by human occupants and optical processing to count and spatially resolve the location of occupants in a room, allowing ventilation flow rates to be properly controlled and directed, if enabled. Occupant detection and counting cheaply and reliably without moving parts is the holy grail of building controls at the moment, which are the basic design principles behind the disclosed inexpensive, static, and stable thermographic occupancy detection sensor.