Pablo
G forces
The rotors outside dameter is 60 cm. the shaft is much less probably under 10 cm. so the g forces will be much less there.

Magnetic fields
The rotor magnetic fields will apear almost stationary to the rotor , but the stator induced fields will not.

Output
output could be via rf link but will be the most interesting problem if direct mounting is selected.

detection
Hall effect, photo reflective or vibration signature are alternatives to direct on the rotor. Use the built in winding to power leds and use a stationary photo detector to detect the leds. no rotation no lit leds. Also of course no output either so a simple voltage sensor on the generator side of the disconnect will also detect rotation.

The main question is why are you trying to detect rotor movement? Do you want to know if the mechanical coupling has failed or the rotor is loose on the shaft,or are you concerned that the prime mover has failed? each of these has an optimum solution so please fill in the blanks for us Regards Terry