OK, I am pretty sure this is an easy project and I am kinda just adding it as an idea.
So a client of mine (Same one I will be putting the intercom into) has two public single occupancy washrooms with electric door strikes, which are controlled by one of many possible cashiers.
sooooo, I ran wires for a ceiling mount Motion detector, a recessed door contact and an indicator LED above each door to each washroom.
the logic being
IF door contact open followed by motion detected followed by door closed and more motion, someone is in the washroom.
IF on the other hand, there is motion followed by door open followed by door close and no more motion after 3 seconds, then the washroom is not occupied.
The purpose of this is to ensure the person pressing the button knows which washroom is available and cannot unlock an occupied washroom accidentally. Oh ya, the door strike unlock button will be bypassed if the washroom is in occupied status.
as a safety feature, I think I will make the light flash, or maybe trigger an indicator in the managers office is the washroom is in occupied status for too long. maybe someone passed out or maybe there is a fault in the system.
what product would you recommend for this? it really only needs 2 or 3 inputs and 2 outputs per unit. I could use one unit to cover both washrooms, but I am thinking of making this as a one room per board application. I haven't decided if I will have the Arduino control the door strike.... probably would simplify things.