Which device is NOT classified as a required distress signal for boats over 16 feet?

Sound signals are not classified as a required distress signal for boats over 16 feet, while the other options are explicitly designed for signaling distress situations. Boats over this length are required to carry certain visual and auditory distress signals to comply with safety regulations.

Rocket flares and daytime flares are both visual distress signals that aid in the identification and location of a vessel in distress, providing crucial visibility over significant distances. These are often mandated for vessels to ensure that they can signal effectively during both daytime and nighttime conditions. Additionally, having three working signals available for use at both day and night is a standard requirement to enhance the likelihood of rescue in an emergency situation.

In contrast, while sound signals can be useful for communication, they do not fulfill the specific requirements of visual distress signaling that can be detected from a distance in emergency scenarios.