The V-2971 (Call Switch) and the V-2970 (Emergency/Normal Call Switch with Volume Control) are designed to be used with the V-2924A and V-2925A Intercom Units. The V-2970 emergency button converts a single button press into the four switch closures required to generate an "Emergency" class of service call.

When the black button is pressed, the V-2971 produce a momentary closure for calling into the V-2924A. The V-2970 also provides an "Emergency" call-in signal (4 interrupted momentary closures) when the red button is pressed.