Tell wheter connected to PC --or-- Project (how?)

I have a small project with a lot of reeds, some LEDs, a speaker or two and other NO contacts. All of them can be open or closed at a given time (otherwise they wouldn’t serve purpose). I need a way to check if hooked to these or the PC, running IDE.

Point is to shut the thing up when in bedroom without changing a flag in the code every darn time I test or deploy. I was thinking along lines of Serial… since that isn’t on the project.

Nevermind I put two things that are usually opposite and put it in Setup.

 if ((digitalRead(pb7) == LOW) && (digitalRead(dr7) == LOW)) hookedUp = 1;
 if (hookedUp == 0) {
   Serial.begin(9600);  // Serial flag - serial doesn't run on Project.
 }

Serial is also disabled for the fact my project has LOTS of connections and 0 & 1 are finally connected.