Jan 2020 was the deadline for aircraft (not ultralights) to get equipped with ADS-B. It transmits location, altitude, ID, what you had for lunch, and other bits to every other aircraft and internet eyeball on the planet. If you can deal with the privacy issue, it’s an awesome technology that will REALLY improve collision avoidance. Eventually.
It’s not cheap, but is still cheaper than going down in flames while listening to all those annoying, screaming, soon-dead airplane occupants.
There’s a portable option for drone pilots and hopefully we can get something for our use or adapt theirs. For more information, go here.