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flag alarm[′flag ə‚lärm]
A semaphore-type flag in the indicator of an instrument to serve as a signal, usually to warn that the indications are unreliable.
A small brightly colored plate inside a certain airborne navigation, or a flight instrument, that comes into view to indicate the malfunction of a system or the instrument itself. It also can indicate that the signal strength or quality of the received signal has fallen below the acceptable values. Also called a flag alarm.