[comboy]

It could activate after ejection, certain acceleration pattern (i.e. crash) or could start broadcasting only after receiving very specific signal (one-time code) on a specific frequency. There are probably plenty more options, it doesn't seem like a hard problem from engineering standpoint.

[MagicMoonlight]

If you’ve gone down you probably don’t want the plane to be announcing it because that will tell the enemy where your pilot and hardware is.

There’s pros and cons to the enemy finding you but generally I’d imagine you want to give the pilot the chance to escape.

[outworlder]

Civilian aircraft, even 2 seaters, have had ELTs for decades. They are being replaced with better systems, but they were designed to do just that: broadcast a signal on a specific frequency after a crash.

Doubtful you want to broadcast the position of the latest generation stealth fighter, however.

[comboy]

As mentioned, it can be silent until receiving specific signal. It can be single frequency it can be multiple, but if it's specific string of bytes or specific timing it's practically impossible to brute force when it's long enough, and when looking for the plane you can broadcast it with high intensity because it is only single use.