Presence Sensor
Last updated: August 13, 2026
A presence sensor detects whether a person is in a room, including someone sitting perfectly still, usually with mmWave radar rather than the heat-and-movement detection of a traditional motion sensor. The payoff: lights that don't switch off while you're reading on the couch.
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A presence sensor answers "is anyone actually in here?" rather than "did something just move?" Most use mmWave radar, which picks up tiny movements like breathing or a turning page, so it registers a person who's sitting still. That's the key difference from a motion sensor, which relies on infrared heat crossing its field of view and "loses" you the moment you stop moving.
This makes presence sensors the backbone of good occupancy automation: lights and climate that follow you room to room and never cut out mid-couch. Many expose distance and zones, and they pair well with Home Assistant and Zigbee setups for local, low-latency reactions.
The reality check: radar is sensitive, so fans, pets, curtains, and even next-room movement can cause false triggers, and dialing in the sweet spot takes tuning. They cost more than PIR sensors and draw more power. For a hallway where any motion is fine, a plain motion sensor is cheaper and simpler.
Related Terms
Home Assistant
Home Assistant is an open-source home automation platform that runs locally on your own hardware, giving you complete control over your smart home without relying on cloud services. With 2 million active installations and 21,000+ contributors, it's become the de facto standard for local-first automation.
Local Control
Local control is when your smart home devices operate entirely on your local network without requiring cloud servers or internet connectivity. Your commands stay on your network, devices respond instantly, and when Amazon's servers go down or a company kills their cloud service, your lights still turn on. Ownership vs renting.
Zigbee
Zigbee is a low-power wireless mesh networking protocol that connects smart home devices like sensors, bulbs, and switches. It's been quietly running smart homes for over a decade, offering excellent battery life and a self-healing mesh - unlike Wi-Fi gadgets, your Zigbee motion sensor won't need new batteries every month.