Or, High Side switch with PNP/P-channel MOSFET (vs low side switch with NPN/N-channel MOSFET).
Generally has the disadvantage that the Gate Off voltage has to equal the source voltage, and turning it on requires pulling to Gnd. If Arduino was 3.3V limited, then another transistor would be needed to buffer the 5/6V to the Gate. I don't know if the PIR can tolerate 5-6V, or if similar buffering would be needed (consisting of NPN transistor with open collector output wired to the gate - PIR/Arduino drives base high, turns on NPN and collector is connected to Emitter/Gnd to turn on the PNP/P-Channel MOSFET.