16ohm Internal Sounder in Konnected?

I pulled out the multimeter and found the following:

  1. When making a “quiet warning”, the voltage supplied is around 0.5v.
  2. When making a “loud alarm”, the voltage supplied is around 2v.

Is it fair to conclude that the volume is driven by voltage?

Given the complexity I will use the supplied piezo buzzer for the “quiet warnings”.

What would be the best way to incorporate this internal speaker to sound with the external siren? I believe it’s just on/off so it would ideally be connected to a switchable output (unfortunately I’ll be using both ALRM terminals already for the external siren and strobe respectively, so I think that counts OUT2 out?).

(a possible solution includes getting a new siren a la UK siren options?)