well i think it might not be so SMOP, best guess I didn't explain myself correctly. What i want is a circuit that is off, no power nothing literally switched off. Then you can switch it on, and off again, no problem. But if it is on AND the PIR is armed say (maybe even not detecting motion but ready to) then the switching the switch off does nothing, power remains on... i know a switch is a literal cut of the circuit but I would like to think there is a way to short circuit if it makes sense. Though could be simple, but then I don't think I can do it all in code...i would need some thing to keep the voltage going when the switch is on AND the system is armed... even if someone flicks the switch off...
no clue what circuit magic I would need. I would google the crap out of this but not even sure what the name of such a switch is called?
What you could use is a simple relay where the relay's contact are wired across (in parallel) the manual power switch. This relay would be controlled by an arduino which would know via some input condition (that the PIR is armed) if it should force the external circuit to be stay turned on by activating the relay or instead let the manual power switch turn the power off. I'm just not convinced you have well stated all the possible states for the external circuit. When should the arduino allow the circuit to be powered off by the manual power switch? Isn't a PIR always 'armed' if it's powered on?