This is also my preferred flight tracker. It’s important to understand how and why this site is available for free, and where the data come from:
the FAA and others mandate that pretty much all aircraft broadcast ADS-B info automatically on every flight. ADS-B is an international standard for aircraft data to be broadcast for the purpose of conspicuous ID, locating, and other info about the craft. Only highly sensitive military flights are exempt, for obvious reasons.
This particular site merely aggregates data from volunteers who have set up stations. These stations are easy enough to set up that there are enough volunteers to provide continuous, overlapping coverage in most places. If you wanted, you could set up a station of your own (requires just a cheap ~$30USD SDR, an antenna, and a laptop/raspberry pi/etc)
This is also my preferred flight tracker. It’s important to understand how and why this site is available for free, and where the data come from:
And that SDR is a hobby in and of itself. There are all kinds of interesting transmissions you can receive from around the world.
Oh, yeah, that’s a whole rabbit hole that I’ve been on for 5 years and counting, and I still feel like I know nothing :)