The dongle is what’s monitoring the traffic. You can get one on Amazon for $25. Here’s mine: https://www.amazon.com/RTL-SDR-Blog-RTL2832U-Software-Define...

I use airplanejs to display the airplanes overhead: https://github.com/watson/airplanejs

There’s a ton of other interesting stuff you can do with the dongle, too. Here’s a great place to start: https://luaradio.io/new-to-sdr.html