wvmarle:
A p-channel MOSFET (like PNP transistor) is for switching high side (positive line of a battery/power supply).An n-channel MOSFET (like NPN transistor) is for switching low side (negative line of a battery, GND of a power supply).
Also the gate voltage has to be handled accordingly.
One last thing:
I didn't think about this solution first, but in order to use my OR gate (and avoid buying a new NOR gate), I could also place the transistor (N-channel, but with a low enough VGS(TH) value) on the ground line back to the batteries, no ?
Like this:
Is there a reason to prefer a solution over another ?
I believe this would work as well, and I would only have to replace the transistor.
wvmarle:
Look for "logic level" MOSFETs. Much more info about this you can find on the sites of Adafruit and Sparkfun. They also have such parts for sale.
Thank you for the advice, I will go have a look ! 