Many headphones, including AirPods, have the capability to act as a Morse transmitter by sending commands with different presses – one for pause or resume, two for the next track, and three for the previous track. With this innovative feature, users can input Morse code using their headphones. For example, a single press with AirPods sends a dit (.), a double press sends a dah (-), and a triple press deletes the previous character. Users can convert these signals into letters or numbers once a delay time is reached. It’s important to note that shorter delays can allow for faster input but may also lead to more errors. Controversially, Firefox has some issues with handling headphone events.
https://github.com/EtherDream/headphone-morse-transmitter