Ringdown

The last ringdown telephone exchange in the United States was located at Bryant Pond, Maine, had 400+ subscribers, and converted to dial service in October 1983.

In telephone systems where calls from distant automated exchanges arrive for manual subscribers or non-dialable points, there often would be a ringdown operator (reachable from the distant operator console by dialling NPA+181) who would manually ring the desired subscriber on a party line or toll station.

In the wire spring relay key service units of the Bell System 1A2, a model 216 automatic ringdown was used to operate the circuit.

The PBX does not offer dial tone to the calling extension: it only detects on-hook or off-hook status.

Private line automatic ringdown (PLAR) is a type of analog signaling often used in telephone-based systems.

When a device is taken off-hook, ringing voltage is automatically applied to a circuit to alert other stations on the line.