Where to Place Motion Sensors in Your Smart Home (And Where Not To)

Motion sensors are the unsung heroes of any smart home. They're what make lights turn on when you walk into a room, send alerts when someone's at the back door, and trigger your "away" routine when the house is empty. But stick one in the wrong spot, and you get lights flickering at 3 AM because your cat walked past the sensor.

Let's go room by room and nail the placement so your automations actually work.

The Golden Rules of Sensor Placement

Before we get into specific rooms, here are three rules that apply everywhere:

1. Height matters. Most PIR (passive infrared) sensors detect best when mounted 6-7 feet high, angled slightly downward. Too high and they miss movement close to the floor. Too low and pets set them off constantly.
2. Avoid heat sources. PIR sensors detect changes in infrared (heat) radiation. Place one near a heating vent, sunny window, or fireplace, and it'll trigger from temperature changes, not people.
3. Face the path of travel. PIR sensors detect movement across their field of view much better than movement directly toward them. Mount sensors perpendicular to where people walk, not facing them head-on.

Room-by-Room Placement

Hallways and Staircases

This is the easiest win. Mount a sensor at each end of a hallway, about 7 feet high on the wall. For staircases, place one at the top and one at the bottom. Trigger: lights on at 30% brightness after sunset, off after 2 minutes of no motion.

Hallway sensors also double as "presence detection", if nothing moves in any hallway for 30 minutes, you can safely trigger your away routine.

Kitchen

Kitchens are tricky because of heat. The stove, oven, dishwasher steam, and even a hot coffee pot can trigger false readings. Mount the sensor on the wall opposite your cooking area, aimed toward the entrance. This catches you walking in without reacting to the oven preheating.

Living Room

The living room challenge: you sit on the couch for two hours watching a movie, barely moving. A standard PIR sensor thinks the room is empty and kills the lights.

Solution: use a PIR sensor for entry detection (mounted near the doorway) combined with a mmWave presence sensor for occupancy (mounted on the ceiling, centered over the seating area). The PIR triggers the lights on, and the mmWave keeps them on as long as someone is sitting there.

Bathroom

Mount the sensor near the door, facing inward. Set a longer timeout (10-15 minutes) because showers create a "dead zone" where steam can confuse PIR sensors and you're behind a curtain anyway. Some people add a humidity sensor that keeps the exhaust fan running until moisture drops below a threshold.

Garage and Outdoor Areas

For garages, mount sensors high (8+ feet) and angle them to cover the walking path from the car to the house door. Outdoor sensors need to be weather-rated (IP65+) and positioned to avoid direct sunlight, which causes false triggers at dawn and dusk.

Common Placement Mistakes

• Behind furniture: Sensors need line of sight. That bookshelf blocks infrared just as well as it blocks light.
• Directly above HVAC vents: Warm air blowing across the sensor creates false triggers constantly.
• In corners pointing at the wall: You lose half the detection area. Center the sensor on a wall with a clear view of the room.
• At pet height: If you have dogs or cats, mount sensors above 5 feet and angle downward. Many sensors also have "pet immunity" settings for animals under 40-60 lbs.

How Many Sensors Do You Need?

For a typical 3-bedroom home: one per hallway (2), one per bathroom (2), one for the kitchen, one for the living room, one for the garage, and one for the front door area. That's about 8 sensors. At $15-25 each for Zigbee models, your total investment is $120-200 for whole-home motion coverage.

Start with hallways and the most-used rooms. Add more as you figure out which automations you actually use daily. There's no rush to wire up every corner on day one.