A Blue Alarm is a signal sent by the remote DS1 endpoint when it is out-of-service. The Blue Alarm Inquiry Test checks the Blue Alarm status of the remote DS1 endpoint.

When a local DS1 board detects a Blue Alarm signal from the remote DS1 endpoint, it transmits a Yellow Alarm to the remote DS1 endpoint and sends a BLUE ALARM message to the system. When the Blue Alarm is confirmed, the system places all trunks or ports of the DS1 board into the out-of-service state. The inquiry test runs every 10 minutes until the Blue Alarm is cleared.

When the Blue Alarm is cleared, the DS1 board stops transmitting the Yellow alarm and places the trunks or ports back into the service state they were in before the Blue Alarm occurred.