Just received these today and loaded two 9v batteries into the enr unit.
Not having an intercom handy, I tried pushing the ON button and get a green
battery indication while the button is depressed, but the unit turns off
when the button is released. There is no aural indication of enr
activating. Does an active headset like this need to be plugged into an
intercom before the enr kicks in?

Mike in Tucson.