I used the pin DI0 to control a 2N39004.
The XBee is 868 Pro (EOL).
If there is a fault in the voltage regulator, the XBee reaches 12V, so the XBee dies.
But that does not end my problem, because the above I can solve with a protection for overvoltage, up to 3.6V. (Zener, Polyfuse or similar).
The major problem to me is that when XBee is broken permit the current flow and allows to pass the current and therefore passes the current through the 2N39004 and switches the cables connected to the relay. In short, DI0 always stays High.
It's possible to do something for if the XBee is broken, the DI0 pin is always Low.