How do you signal danger on a whistle or horn?

To signal danger using a whistle or horn, the appropriate response is to use five or more short blasts. This signaling convention is recognized internationally as a call for assistance or a warning of danger. The five or more short blasts are designed to attract attention in a clear and unequivocal manner, distinguishing it from other sounds that might be made in a normal situation.

Using fewer than five short blasts, such as three or fewer, may not convey the urgency or specific meaning of a distress signal and could be misconstrued as a standard communication signal. A single long blast is typically used to indicate a vessel's presence or to communicate maneuvers rather than signaling distress. Continuous sounds, while possibly drawing attention, do not conform to the agreed-upon signaling protocols for danger and could be considered ambiguous.

Therefore, five or more short blasts effectively communicate an emergency or the need for assistance, thus ensuring a timely response from nearby vessels or personnel.