All our newer trucks have them. No one seems to even know what they are let alone use them. We also have a phone intercom with buzzer. Never once seen it used or heard of it. Both systems are accessed from the airway seat and if I've going to get up and move to that seat to use them, I might as well stick my head through the pass through and talk to my partner. Besides clear communication is more important, I can say more with a "Hey Mike, why don't we make that a Code 4 return now please." Being calm and professional when things are coming apart is going to do far more to calm the Pt. and family then little tricks and signals.