I ditched motion sensors for mmWave radar, and my lights never plunge into darkness anymore

Published Sep 12, 2026, 5:00 PM EDT Jasmine is Software and PC Hardware Author at XDA with years of tech reporting experience ranging from AI chatbots right down to gaming hardware, she's covered just about everything. Whether it's breaking news about the latest AMD NPUs or creating video tutorials on social media platforms, Jasmine has contributed to the world of AI and tech in a variety of ways including interviewing the CEO of Razer, AMD's Director of Product Marketing and the VP of Lenovo. Passionate about gaming and PC technology, she has built countless computers, keyboards and other peripherals - knowing them inside and out. For so many smart home builders, the reality is you're sat at your desk or on the sofa reading an article or watching a movie, and suddenly the room plunges into pitch-black darkness. You're forced to vigorously wave your arms around just to trick a wall sensor into turning the lights back on. Traditional motion sensors fail because passive infrared sensors don't actually detect presence; they detect radiant heat in motion. The moment you sit still, the delta in infrared radiation drops to zero. To the PIR sensor, the room is completely empty. There are workarounds, but these are messy, like bumping timeout intervals to 20 or 30 minutes, which can waste energy, or adding multiple PIR sensors at odd angles. True occupancy automation requires replacing binary motion triggers with an interlocking presence engine by combining mmWave micro radar, sub-meter Bluetooth, and RSSI beacons and hardware state telemetry inside Home Assistant. You can build a zero-latency, unbreakable presence tracking matrix that never plunges you into darkness again. Traditional presence sensors suck The technology feels outdated The physics and silicone differences between legacy infrared detection and modern active sensing are the reason why PIR failed and the reason why mmWave radars replaced it. PIR, or pyroelectric sensors, rely on a Fresnel lens splitting a field of view into zones. It requires an object with a surface temperature different from the ambient room temperature to physically cross from one optoelectronic zone to another. If you don't cross the field of view, you're technically invisible. With mmWave sensors, they operate at 24GHz or 60GHz, and the sensor broadcasts high-frequency electromagnetic waves and measures the Doppler phase shift of returning reflections. It detects micro-movements down to fractions of a millimeter, including the physical rise and fall of your chest while breathing or the pulse at your wrist. This means that even if you're not actually moving, the natural movement that your body makes ensures that the sensor detects that you're there. Alongside this, a lot of modern multi-target radar sensors don't just output a binary occupied (yes/no) feed. They instead stream real-time coordinates, allowing Home Assistant to draw virtual zones around a couch, bed, or desk for even further automation. You don't just have to opt for mmWave There are so many ways to detect presence No-motion presence engines have a range of uses and can be used in many ways. While they continue to track you without you needing any traditional motion sensors, the first is obviously continuous micro presence via the mmWave radar, which sets the baseline. You can place these sensors strategically in living areas, offices, and bedrooms, and they'll capture static motionless occupancy even when you're reading, working, or sleeping, with zero timeout delays. You can combine this with identity and microlocalization via BLE beaming. mmWave doesn't know who is in the room even though it can tell a human is there. The fix is to deploy a $4 ESP32 node running ESP Presence or use Home Assistant's Bermuda BLE triangulation. It can then track the Bluetooth Low Energy advertisement signals from a smartwatch or your phone. That way, the house can calculate signal distance by measured RSSI values and determine who's in the room. As a result, the office doesn't just illuminate; it actually loads your specific lighting preferences and desk type presets because it detects your watch within a 1 m radius. An issue you might encounter is that if you sleep under a thick down duvet, even 60 GHz mmWave radar can occasionally miss shallow breathing if it's obstructed, or ceiling fans can cause phantom false positives. The fix here can be inexpensive automotive weight sensor mats or DIY load cells tucked beneath the mattress or desk chair cushion. Then you can ensure that sitting down or lying in your bed asserts a definitive physical binary state that overrides all optical and radar logic. Inferred state telemetry is a great way to track presence in a room as well, so that you can be 100% certain that where you are in the house is tracked regardless of any of your sensors. You can do this by using `hass.agent` on your desktop, which monitors active user input (like mouse or keyboard use) or even just an active session state. Or you can use smart plug power monitoring on your TV or gaming PC. That way, if either of these is drawing a certain amount of wattage, the living room occupancy state is pinned to occupied, regardless of whether anyone is moving in front of a sensor. So what hardware do you need? Everything is cost-effective What hardware should you be purchasing in order to deploy these automations? The main thing worth investing in is the radar itself. You can pick up a cheap radar module for less than $10 on AliExpress and pair it with an ESP32 or a pre-packaged commercial unit like the Aqara FP2 or Apollo Automation MS-2. In total, these are extremely cost-effective and allow you to ensure you have constant presence detection. Invest in a room beacon. Flash existing spare ESP32 boards with ESP Presence and drop one in each key room to ingest smartwatch BLE advertisements. If you do want to take advantage of the chair/bed hack, then buying a $6 12 V automotive seat occupancy sensor and connecting it to the GPIO pin of an existing USB home node (with an internal pull-up resistor) before sliding it under the cushion of your desk chair will ensure that any time you're sat down, a sensor can pick up on it and therefore knows that the room is occupied. Make your smart home work for you Don't sit in darkness A smart home shouldn't force you to change your physical behavior. The moment an automation demands that you wave your hands, shout at a voice system, or open a phone app, the technology has essentially failed. Instead of using cheap plastic PIR motion sensors that keep leaving you in the dark and require you to wave your hands around like you're a circus, you can build a multi-layered presence engine with radar, contact telemetry, and local radio beacons that make your smart home behave like it actually knows you're there.