This is an especially useful feature when using any DUPLEX board. There is a long delay between pressing PTT and the duplex board locking in on the signal. This alert tone will play once it is locked. You learn to listen for this tone before talking. Once you get the hang of it you wonder how you lived without it. Here is a link to a YouTube video on how to set it up on an AnyTone 878.
https://youtu.be/noLc97ZcKaQ?si=0RzRSSxJicjwEe-M If you have any trouble please just Email me at dave@n5boc.com
David