If the sensor is a simple open/closed contact, such as a door or window contact, it needs no external power. The zone terminals produce a voltage to sense whether it is open or closed.
For powered sensors, such as motion or glass break detectors, you can use VAUX from the M1 to power them. But you need to do a current load calculation to make sure all the devices powered by the M1 do not require more than a total of 1 Amp. For smoke detectors, you should power them from SAUX.
If the M1XIN is in a remote location from the M1, you will probably need to use an auxiliary power supply to power things. Or, you could run an extra pair of wires back to the M1 to provide power from VAUX, but in a large system, you will probably need an aux power supply anyway.
