When I first started, back in the 1930s - had a Lt. tell me when he was a rookie, they tried (didn't last long) a flip switch in the horse drawn carriage - that would open the mic so you could talk hands free, making traffic stops and pursuits especially much easier. He said that idea was a bad one because too many forgot to switch back off, and you can imagine the rest. I remember him saying it was somewhere up, like maybe even the headliner area, so it wouldn't get accidentally flipped.