Hello Simone,
I know that the NXP Magnetometer, the MAG3110, has been tested to detect presence of AC voltage due to the electromagnetic field generated, however, test results are very variable.
It will depend on where you need to measure the voltage, for example, using the MAG3110 you can easily detect (after proper calibration) the presence of AC voltage directly measuring in the AC cables, but it is very hard to detect presence of it through the walls.
So, as a conclusion and to be honest with you, I would say that it is possible to detect the presence of AC voltage using a Magnetometer, but it is not reliable.
I hope this information helps.
David
