MONAD FLEET · NODE 06
Howdy — you found a
Wi-Fi sensing node.
This little box is listening to the shape of the radio waves in this room. Not to what they carry — to how they bend. When people move through a space, they bend Wi-Fi in ways we can measure, and that is enough to estimate how busy a room is without watching anyone.
monad06 · Raspberry Pi 5 + Intel AX210 · FIIT STU
What it is doing right now
Reading the node…
Why it is here
Counting people indoors is genuinely hard. Cameras work but are invasive, turnstiles only see doorways, and phone-based tracking needs everyone to carry the right app. This fleet is testing a fourth option: read the Wi-Fi signal itself.
Every Wi-Fi radio already measures Channel State Information — a fine-grained picture of how a signal arrived, across dozens of frequencies at once. A body between two radios changes that picture. The research question is how far you can push it: how many people, how reliably, in a room nobody instrumented in advance, using hardware that costs about as much as a textbook.
That is a PhD's worth of question, and this fleet is how it gets answered with real measurements instead of simulations.
What's inside the box
Four parts, and only one of them is actually a radio. Open any of these for the numbers.
Raspberry Pi 5 A credit-card-sized Linux computer — the brain of the box.
Quad-core Arm Cortex-A76 at 2.4 GHz, 8 GB of RAM. It is the first Raspberry Pi with a real PCIe slot, which is the only reason this sensor is possible at all — everything below plugs into that one slot. Its own Wi-Fi chip is only ever used to log in and report home; it cannot measure CSI.
Intel AX210 A Wi-Fi 6E radio chip — the part that actually senses.
The same class of chip as the Wi-Fi in a recent laptop, on a fingertip-sized card. Every packet it hears, it also reports back how it arrived — up to 996 separate frequency slices at once, measured on this exact card at a sustained 608 measurements a second. That fine-grained "how a signal arrived" reading is Channel State Information: the thing this whole fleet is built to read.
M.2 HAT + two antennas The adapter card that lets the radio talk to the Pi at full speed.
A small carrier board that turns the Pi's PCIe slot into a socket the AX210 card can plug into, plus a short ribbon cable between the two. Two stick antennas run off it — both have to be connected, or the radio quietly halves its own resolution and nobody watching the box from outside would know.
Industrial microSD card Where the measurements are written, built to not wear out.
An endurance-graded card rated for continuous writing, −40 °C to +85 °C, and roughly 5,900 TB of total writes over its life — because this box is meant to sit recording for weeks at a time, unattended, and a card built for a dashcam is not built for that.
Curious how it's wired together?
What this sensor does not do
- No camera. There is no lens on this device.
- No microphone. It cannot hear anything.
- It does not know who you are. It records a physics measurement of the room, not identities, not device addresses of people passing by, not what anyone's phone is doing.
- It is not reading your traffic. Channel state is the radio equivalent of noticing a room got warmer — it carries none of the contents of anyone's connection.
Placed and operated by the Faculty of Informatics and Information Technologies, Slovak University of Technology, for doctoral research. Questions: jakub.dubec@stuba.sk
What is running here
These are the short, defined walks volunteers run at this node so a measurement has a known answer to check against.
Quests offered at this node
- Study session Do nothing, on purpose, and get credit for it. Tell us roughly how long you are staying, then go back to pretending to read.
- Ready to run here.
- Fingerprint Stand perfectly still for thirty seconds, like a Victorian having their portrait taken. The radio needs a moment to get a good look at you.
- Ready to run here.
- Treasure hunt 10 grey boxes are hiding in plain sight around the library. Find them all and you will have walked the single most useful lap anybody can walk in here.
- Ready to run here.
- Counting Wander the library and count the humans. You are the ground truth; the radio is the one being tested.
- Ready to run here.
- Survey loop One fixed lap of both reading rooms, ending where it began. Dull by design — the same lap walked on four different days is worth more than four different laps.
- Ready to run here.
- Survey loop (tracked) The survey lap with the handset tracking its own path. Operator take: it holds the camera and the battery, and it is the only run that yields a positioning error rather than a position.
- Ready to run here.
Want to help it learn?
The experiments need something the radios cannot supply on their own: ground truth — a trustworthy record of how many people were actually in the room. That comes from volunteers walking a short, defined route while the node records, so the measurement has a known answer to be checked against.
The companion app that runs those walks is in closed testing at the faculty and is not on the app stores yet. If you are at FIIT and want in, or you are just curious what the data looks like, get in touch.
Ask about taking part See the experiments
If you take part, an account stores your email address and which nodes you have visited — nothing else, and you can ask for it to be deleted at any time. Measurements you contribute are kept pseudonymously for the research.
The rest of the fleet
10 of these are deployed, and each one sees a different slice of the same building — which is the whole point: one sensor sees a corridor, several see a floor.
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