Infra-red occupancy sensors are triggered through the movement of passing heat sources between the segments of its lens. These sensors by nature are less sensitive to radial movement – back and forth from the sensor; but are more susceptible to tangential movement – movement around the sensor. The benefit of using an infra-red occupancy sensor is that it cannot detect through soft furnishings, and is limited to sensing in line of sight. One such scenario is that if it were to be placed inside a building with multiple rooms next to one another, it will not detect occupants within the room next door – whereas the microwave sensor would. Therefore this sensor is highly beneficial in scenarios where one would only like the detection to be within the room it is placed.

The negative of using an infra-red occupancy sensor is that it cannot detect through soft furnishings such as that of wood, glass etc. What makes it beneficial can be its weakness in some scenarios. For example, a public restroom would require an occupancy sensor to detect occupants within the cubicles – the infra-red could not detect the occupants and will therefore not work in such a scenario. Another negative is that it is susceptible to air turbulence, which is caused when hot air and cold air intermingle, which would cause the sensor to trigger. This means that the sensor may not be placed nearby to air-conditioning units or heaters etc.