This orange wire controls the buzzer for my intercom unit, reckon if I put a resistor between it and the screw it would lower the volume of the buzzer?
That sounds cool but I only have resistors ATM, and regardless to change the volume I would need to hide it under the casing since this is a "stealth" modification that my apartment doesn't know about
It depends if it's a voltage that's triggering the speaker via a circuit on that IC, or if it ends up powering the speaker directly, and I'd bet the former. Putting a resistor in series with one of the speaker leads is more likely to achieve what you're hoping for (without knowing more about the circuit).
Do voices and the buzzer sound come out of the same speaker shown in the picture, or is there a separate little "buzzer" speaker in there?