Partyline Subscriber Polling Alarm:

With this option the Central Office unit (C.O.) polls up to eight (8) Partyline Subscribers for link integrity. Every three hours the C.O. polls all Subscribers of the system in a serial fashion by sending a poll request starting with the last Subscriber. The C.O. unit is equipped with an alarm board that provides up to eight (8) dry relay contacts to indicate which Subscriber in the system does not respond to a poll.

RT 9000 poll alarm (PDF)