Consequences

• The system takes responsibility for initiating the use case.
• The system can pass information about the alarm to the actor.
• The actor does not have to interrupt their current task immediately to respond to the alarm.
• The actor can ignore the alarm.

If the alarm is important, you may need to include a Confirming Step (3.6):

This variant has the following different consequences to the main pattern:

• The actor cannot continue with their current task: they must interrupt it to confirm the alarm.
• The actor cannot ignore the alarm.

Alarm use cases can often indicate (potential) violations of business rules -- say that a performance should not continue if less than 15% of seats have been sold by the time it starts.