Ten bell alarm

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A ten bell alarm is a full line of asterisks on the display of a teletype machine.

The teletype machine had an internal bell, sounded by a special "Bell" character, which was activated ten times in rapid succession, immediately after a full line of X's, as part of an EBS test or an actual EBS activation message. Ten Bell Alarms were used in wire services (such as AP) when news was transmitted via teletype. A ten bell alarm on a teletype message would indicate an activation of the EBS, and would alert the proper parties.

There was also a five-bell alarm used for tornado warnings.