mmWave vs Wi-Fi sensing.
Both detect people by how a body changes a radio signal. An mmWave sensor is a small radar that sends its own signal, mostly at 24 GHz or 60 GHz in smart home sensors. Wi-Fi sensing analyzes the Wi-Fi signal between devices at 2.4 GHz or 5 GHz, using Channel State Information (CSI).
The difference in frequency explains most of what follows. It decides how small a movement each one sees, whether it works through a wall, and how many devices a home needs.
At a glance
Two technologies, good at different things.
mmWave
Wi-Fi sensing
In detail
Movement, zones, and range.
mmWave sees the smaller movement.
A shorter wavelength turns a small movement into a bigger change in the signal. mmWave works with a wavelength of a few millimeters and Wi-Fi with several centimeters, so mmWave picks up much smaller motion, including a very shallow breath. Someone sitting completely still is still detected.
Wi-Fi sensing needs a larger movement.
The chest has to move with the breath. Normal breathing, fidgeting, or typing on a keyboard is enough. Hold your breath, or breathe very shallowly, and Wi-Fi sensing might not pick you up.
Smaller motion
Chest movement
mmWave can draw tight zones.
To place someone in a room, a sensor needs the direction a reflection comes from and how far it travelled. Direction takes several antennas that are phase coherent, and distance depends on bandwidth. mmWave sensors built for zones, like the LD2450 or the Aqara FP2, have several transmit and receive antennas and a wide band, so they can report a position and draw tight zones around a desk, a patch of floor, or the sofa.
Wi-Fi sensing zones are room level or proximity level.
Wi-Fi devices in a home have few antennas and narrow channels compared with an mmWave sensor built for zones, so they cannot reliably tell where in a room someone is. Zones come from where the devices are placed instead. A zone covers either the area between devices, which is often a room or more, or the area close to a single device. Either way it is not a box around a desk.
Zones at x, y
Near a radio, and between two
mmWave needs line of sight.
mmWave only senses what it can see. Furniture hides the floor behind it, and a wall stops the signal, so the sensor has to be mounted in view of the area.
Wi-Fi sensing goes through walls.
Wi-Fi uses a much lower frequency than mmWave, which passes through walls, furniture, and floors. The devices do not need a view of the room, so they can sit in a cupboard, a drawer, or inside a wall.
Stopped by walls and furniture
Through the wall, from hidden radios
mmWave covers one room at a time.
Most mmWave sensors for the home reach about 6 to 10 meters. Walls block most of the signal, so covering a home takes a sensor in each room.
Wi-Fi sensing reaches across rooms.
Wi-Fi sensing between two devices usually reaches 10 to 30 meters or more, limited mostly by how far the devices keep a strong Wi-Fi connection. It covers the area between its devices, including the walls in between, so a few devices can cover several rooms or a whole floor. Walls still cost something. Drywall, wood, and furniture take little of the signal. Concrete and brick take much more, so expect less range through them.
A sensor in each room
Radios across the rooms
Hardware and cost
A dedicated sensor, or Wi-Fi devices you may already have.
mmWave
mmWave is dedicated hardware. Common choices in Home Assistant setups are the LD2410 and LD2450 modules, the Aqara FP2, and the Everything Presence One. Each sensor covers the area it can see, so it is mounted in a corner or on the ceiling with a view of that area.
Wi-Fi sensing
Wi-Fi sensing reads Channel State Information, which describes how the signal changed on its way between two Wi-Fi devices. Most consumer devices do not expose it, so the sensing runs on hardware that does, like a dedicated Wi-Fi sensor, a router with sensing built in, or an ESP32 board, which costs a few euros and is already common in Home Assistant homes through ESPHome. The other end of the signal can be a Wi-Fi device you already have, like a TV or a speaker. Since the signal passes through walls, the devices can sit out of sight, for example in a cupboard or a switch box.
Recommendation
Use both, each where it fits.
Use mmWave for tight zones and stillness.
We recommend mmWave where a zone has to be tight, or where people are expected to be very still, like lying in bed.
Use Wi-Fi sensing where people move.
Wi-Fi sensing works where people move around, breathe normally, fidget, turn in a chair, or type on a keyboard. That describes most of the home.
Wi-Fi sensing first, mmWave where it falls short.
Cover most of the home with Wi-Fi sensing, and only add a dedicated mmWave sensor where it falls short, like a bed or a spot where someone sits very still. That keeps the cost down, since you do not need an mmWave sensor in every room, and it keeps the home free of sensors mounted in every corner.
Wi-Fi sensing across the home, mmWave at the bed
With TOMMY
Two ways to use Wi-Fi sensing.
TOMMY One is a single device that uses Wi-Fi devices you already have as passive devices. TOMMY Zero turns your own ESP32 boards into sensors.
TOMMY One
PrototypeOur standalone device.
TOMMY One is a single sensor that you plug in and hide, for example in a cupboard. It senses the area around it, and it uses up to 4 Wi-Fi devices you already have as passive devices, like a TV or a speaker, to also sense the rooms in between. Nothing has to be installed on those devices. It has three detection modes, from a single room to the whole home.
TOMMY Zero
Your own ESP32 boards.
TOMMY Zero runs on hardware you bring yourself. The TOMMY Zero server runs as a Home Assistant App or a Docker container. You can create several zones, and each zone covers the area between at least two ESP32 boards with the TOMMY Zero firmware, flashed from the dashboard over USB or through ESPHome.