Motion vs. presence

In home automation, the difference between a motion sensor and a presence sensor comes down to how they detect activity and how “aware” they are of a person in a space. A motion sensor is the simpler of the two. It typically uses passive infrared (PIR) technology to detect changes in heat as it moves across its field of view. This makes it excellent for triggering lights when someone walks into a room, but it has a limitation. Once you stop moving, it may assume the room is empty. Anyone who has had lights turn off while sitting still at a desk knows this frustration well.

A presence sensor, by contrast, is designed to detect sustained occupancy. It often uses more advanced technologies, such as mmWave radar, which can detect even very slight movements, such as breathing or shifting posture. This means it can reliably determine that someone is still in the room, even if they are quietly working, reading, or watching TV. In practical terms, I have set up a presence sensor in my study to turn the lights on when I am in the room and off when I leave. It did detect me in the study when I was actually standing outside in the hallway, but configuring the zones resolved that issue quickly. For me, the presence sensor is much more reliable at identifying when anyone is in the room.