What this is
Every airliner above your house is talking. About once a second, it broadcasts who it is, where it is, how high and how fast. That signal is called ADS-B, it is not encrypted, and anyone with a small radio can listen to it.
This site explains three things, in order: what that signal is, how to build a receiver for it with a Raspberry Pi and a few parts, and how to join the thousands of people who share what their receiver hears with the world’s flight-tracking networks. The fourth part is ZenithBoard: a free program that installs all of it in one go and shows the aircraft overhead on an old tablet, in glowing dots or on an airport split-flap board.
What it costs, what it takes, what it gives
It costs about 60 to 120 €, depending on the Raspberry Pi you choose and the antenna. Nothing after that: no subscription, no account you have to pay for.
It takes about an hour the first time, a Raspberry Pi, a wall socket and your home Wi-Fi. You do not need to know how to program. You will type a few commands, which are given to you.
It gives the aircraft around you, on your own screen, with no one in between. If you share your data, the tracking networks give something back: FlightAware opens a free Enterprise account, Flightradar24 a free Contributor plan, Plane Finder free premium use of its site and apps, and ADS-B Exchange shows your feed on its site. And if you turn ZenithBoard’s sharing on, the aircraft crossing your sky get posted to Bluesky, as a picture of your wall.
The limits, said plainly
A receiver only hears what it can see: the signal travels in a straight line, so a window facing a hill hears less than a roof. A Raspberry Pi with 1 GB of memory is enough for all of it, measured on the author’s own Pi 3B. Wi-Fi works; a cable works better. Nothing here is for sale; the only money that moves is a beer, if you feel like it, at the bottom of the page.