For most of the time I’ve been doing this, “battery-powered presence sensor” was a contradiction in terms. mmWave radar — the technology that can tell a person sitting perfectly still on a sofa from an empty room — drinks power. So the rule was simple: if you wanted real presence detection, you ran a wire. If you wanted a battery, you got a PIR motion sensor and you accepted that the lights would go off on you mid-paragraph because you dared to read a book without waving your arms.
That rule quietly died over the last year, and I’ve spent the past week reading teardowns and reviews to figure out what my own shortlist looks like now. Here’s where I landed — and what I’m actually going to do about it, which is not “buy everything”.
The trick: PIR wakes the radar
The breakthrough isn’t a magically efficient radar. It’s a division of labour. The new generation of battery sensors — Aqara’s FP300 and SwitchBot’s Presence Sensor are the two prominent ones — pair a nearly-free-to-run PIR sensor with a 60 GHz mmWave module that sleeps most of its life. PIR spots you entering the room and wakes the radar; the radar holds the room “occupied” while you sit still; when it decides the room is empty, it goes back to sleep and hands the watch back to the PIR.
Both devices use the same radar chip, a Possumic RS6130, which SmartHomeScene’s teardown of the FP300 found is built around an ultra-low-power mode that lets it stay useful for years on coin cells. Aqara claims up to three years on two CR2450s — for a device that also reports light, temperature and humidity. The SwitchBot runs on ordinary AAAs, which I appreciate on principle; coin cells are the one battery format I always forget to stock.
I want to be honest about the trade-off baked into this design: the radar only wakes when the PIR triggers. Walk-in detection is PIR-grade, not radar-grade, and there are edge cases — a room you enter very slowly, or re-enter within the radar’s sleep window — where the handoff can stumble. Reviewers report it works well in practice. But it’s a duty-cycle trick, not free energy, and it behaves like one.
My 2026 shortlist, by job
Battery, no wires, mainstream: the Aqara FP300 is the obvious pick, and not just because everyone says so. It speaks Zigbee or Thread — you choose — which means it drops straight onto my existing Zigbee2MQTT network with no app, no cloud, no account. Five sensors in one housing (mmWave, PIR, lux, temperature, humidity) also means one battery to manage instead of three separate devices. Derek Seaman’s Home Assistant-focused review covers the setup details well.
Wired, local-first, tinkerer-friendly: the Everything Presence Lite remains the best value in the ESPHome camp at around $35. It’s an ESP32 with a 24 GHz radar that tracks up to three targets with live X/Y coordinates, and because it’s ESPHome, the firmware is yours — no vendor app, no phoning home, updates on your schedule. Apollo Automation’s MSR-2 and R PRO-1 play in the same league; the R PRO-1 even takes Power-over-Ethernet, which is the kind of thing that sounds excessive until you’ve fished a USB cable through a finished wall.
Budget: the Sonoff SNZB-06P at roughly $15 is still the honest cheap option. It’s a 5.8 GHz radar, so it’s less precise than the 24/60 GHz crowd and it has no PIR, but for a hallway or bathroom where you just need “is someone in here, including standing still at the mirror”, it does the job — and as a mains-powered Zigbee device it doubles as a router that strengthens the mesh.
DIY: an ESP32 plus a Hi-Link LD2410 module costs a few francs and twenty minutes of your evening. This is how I first learned what mmWave could do, and the community support in ESPHome is still excellent. It won’t win on looks. It will win on understanding exactly what your sensor is doing and why.
The local-first fine print
A few things I weigh that spec sheets don’t mention. Battery Zigbee devices are end devices, not routers — an FP300 joins your mesh but doesn’t strengthen it, while a wired Sonoff or a plug-in Apollo does. ESPHome devices are the gold standard for ownership: the configuration lives in my Git repo next to everything else, and no firmware update ever arrives without my say-so. And Aqara’s older FP2 — still a fine sensor with its 30 configurable zones — needs the Aqara app for initial zone setup. You can uninstall the app afterwards and run it locally via HomeKit, but “install our app first” is exactly the kind of small concession I’ve been trying to stop making.
Placement matters more than brand, by the way. mmWave sees through more than you expect: a fan, a curtain breathing near a tilted window, even a large houseplant in an air current will hold a room “occupied” all night. Every one of these sensors has sensitivity and zone controls for a reason. Budget an evening of tuning per room, whatever you buy.
What I’m actually doing
Not replacing everything, that’s certain. The PIR sensors in the hallway and the storage room are staying — for rooms you only walk through, presence detection solves a problem that doesn’t exist, and a PIR on a lithium cell will outlive some of my appliances. The office and the living room are different: those are the two rooms where somebody regularly sits still for an hour and gets plunged into darkness for it, and those are the two rooms that justify real presence hardware.
The office already has a wired ESPHome radar and it isn’t going anywhere. For the living room — where my better half has opinions about visible cables that I have learned to respect — the FP300 is the first battery sensor I’d actually consider, precisely because it asks for no wire, no app and no cloud. That combination didn’t exist two years ago at any price. That’s the quiet story of 2026 so far: the compromise between “works properly” and “goes where I want it” is finally dissolving, one duty-cycled radar at a time.
Good roundups if you want to go deeper: SmartHomeScene keeps a continuously updated best-and-worst presence sensor list — including the ones to avoid, which is half the value.
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