PIR vs mmWave: A Guide to Presence Sensors That Actually Work

If there is one point that judges whether a smart home is magic or annoying, it's presence sensors. A false trigger in the hallway is just annoying. A false trigger in the bedroom or a "lights off while I'm here" in the office is... a deal-breaker.

The dilemma today is clear: PIR or mmWave? The right answer isn't "one is better", but: what space do you have and what behavior do you want.

1) What Each Sensor Measures (Simply Put)

PIR (Passive Infrared) – Motion Sensor

PIR detects heat changes (infrared) moving in its field of view. In short: it is excellent at walking/motion, not at "quiet presence".

What it does perfectly:

• You enter a room → it catches you instantly
• You pass through a hallway → lights turn on correctly

Where it struggles:

• You sit still (office/TV) → after a while it might "lose" you

mmWave – Presence Sensor (Radar)

mmWave emits radio waves and detects micro-movements (e.g., small body movements, breathing). This makes it ideal for "I am here" even when you are not moving.

What it does perfectly:

• Office / computer / reading
• Living room (sofa, TV)
• Bedroom (presence without "motion")

Where it needs attention:

• It can "see" through thin walls/drywall/glass
• Needs correct sensitivity and zone settings

2) Pros and Cons (Practical, Not Theoretical)

PIR — Pros

• Simple and proven (mature technology, stable behavior)
• Economical and easy to install
• Usually fewer "mysteries" during commissioning

PIR — Cons

• It is a motion sensor, not a presence sensor
• Needs "timers" to not turn off when you sit still
• In "sitting" spaces, it can disappoint you

mmWave — Pros

• Does what we all want: true presence
• Allows a smart home that feels "natural" (no need to wave your hands)
• Very good for HVAC (occupied/unoccupied) because presence is essential input

mmWave — Cons

• Needs correct placement and tuning (otherwise it "catches" the wrong room)
• Can have false presence (e.g., motion behind a wall)
• Usually more expensive than PIR

3) What Goes Where (The Decision Map)

PIR is ideal for:

• Hallways / entrances / stairs
• WC / storage / auxiliary spaces
• "Walk-through" spaces where motion is guaranteed

Goal: instant ON, short OFF-delay.

mmWave is ideal for:

• Office / home office (sitting, working)
• Living room (watching TV, sitting on the sofa)
• Bedroom (calm presence, small movements)
• Hotels / rooms when you want serious occupancy logic for energy

Goal: not to "lose" presence, so longer OFF-delays and correct zoning.

PIR + mmWave Combination (The "Premium")

In the best projects, we combine them:

• PIR for fast ON (as soon as someone enters)
• mmWave for HOLD (to keep "occupied" as long as there is presence)

This gives the most natural experience and dramatically reduces errors.

4) The 4 Most Common Mistakes (Especially with mmWave)

1. Wrong direction: facing a door/hallway/adjacent room.
2. Oversensitivity: leaving it at "max" to catch everything → catches... everything.
3. No zones (gates): not excluding areas that shouldn't be measured.
4. No timing logic: a proper system needs correct delays, not "instant off".

5) Recommended Logic (Cheat Sheet That Works)

For Lighting

• PIR only (hallways/WC): ON: 0s | OFF: 60–180s
• mmWave only (office/living room): ON: 0–3s | OFF: 5–15 minutes
• PIR + mmWave:
  • ON = PIR OR mmWave
  • OFF = "no mmWave presence" for X minutes

For HVAC (AC / Fan Coil)

• Use mmWave or combination, because "occupied" is critical.
• Better Eco setpoints instead of full OFF (more comfortable, safer for humidity/thermal inertia).

6) Privacy: "Does It See Me?"

Neither PIR nor mmWave is a camera. They do not record images. mmWave, however, is more "sensitive" in detecting presence, so it needs proper design to avoid measuring the wrong space.

Conclusion

• Want reliable "in-out"? → PIR
• Want true presence in spaces where you sit? → mmWave
• Want an experience level of "always works without frustration"? → PIR + mmWave with correct logic