433/868 MHz: the universal receiver for "invisible sensors"

If you own a garden weather station, a wireless thermometer in the fridge, a car with a tyre pressure warning light, or even just a gate remote, you probably already own a small radio transmitter that nobody ever pointed out to you. It transmits on the 433 MHz or 868 MHz bands, licence-free in Europe, and it does so constantly, silently, towards... nobody in particular. Unless someone is listening.

With SDRCrew, now, you can be that someone.

What 433 and 868 MHz really are

They are the two ISM (Industrial, Scientific, Medical) bands most used in Europe for licence-free short-range data transmission: no paperwork, no fee, just a very low power limit. That is why they have become the de-facto standard for an enormous number of low-cost "smart" objects that do not need Wi-Fi or Bluetooth: weather stations, door and window sensors, flood detectors, energy meters, remote controls, and - probably the most surprising discovery for those who do not expect it - the tyre pressure sensors (TPMS) that almost every modern car has fitted as standard.

The problem is that each of these devices speaks a slightly different "dialect": modulation, coding and packet format change from manufacturer to manufacturer. Decoding them by hand, one by one, would be an enormous job.

What SDRCrew's 433/868 module does

The module relies on rtl_433, an open-source project that over the years has learned to recognise hundreds of different protocols, and presents its output in a panel designed to be looked at, not just read from a terminal. Concretely:

It automatically catalogues over 460 known sensor models - weather stations (the largest category, over 210 models), car TPMS sensors (42), energy meters (26), door/window sensors (16), rain, flood and motion detectors, and more. If a device is not catalogued yet, the panel still offers a quick online search on the detected model.

It lists every device seen with ID, model, RSSI (the received signal strength) and, when available, temperature, humidity and accumulated rain.

It keeps a history with a chart for every sensor, so you can see the trend over time (useful, for instance, to find out whether your fridge really holds the temperature it claims).

It lets you rename and locate each device ("Terrace", "Cellar", "Family car"...), so the list stops being a list of hexadecimal IDs and becomes something readable.

It exports to CSV for those who want to take the data elsewhere - a spreadsheet, another analysis tool.

All this with a simple RTL-SDR dongle, the same one you probably already use to listen to the other SDRCrew tabs.

A practical use: what the airwaves around you really "hear"

The first time you start this module in a residential area, a surprise is almost guaranteed: within a few minutes sensors that nobody knew were transmitting appear. Neighbours' weather stations, TPMS sensors of cars parked in the street, energy meters of the building. It is a small reminder of how much more crowded the radio spectrum around us really is than it seems to the naked ear.

Try it yourself

The module is already included in SDRCrew, free like the rest of the project. All you need is an RTL-SDR dongle and a bit of curiosity. If you try it and find a sensor the catalogue does not recognise, or you have an idea to improve it, let me know - contacts are in the app's Info tab. And if the project is useful to you, a coffee to support its development is always welcome.