Which signaling device would be appropriate for both day and night use?

Flares are appropriate for both day and night use because they are designed to produce a bright, easily visible signal regardless of the lighting conditions. During the day, flares generate bright smoke or a vivid flame that can be seen from a distance, making them effective for signaling distress or for attracting attention. At night, the bright light emitted by flares can be seen from far away, enhancing visibility in dark conditions. This dual functionality makes flares a crucial safety tool for boaters facing emergencies, ensuring they can signal for help effectively at any time of day.

While sound signals, flags, and lanterns have specific uses, they do not offer the same level of visibility in both light settings. For example, sound signals are limited to auditory range, flags require favorable wind conditions and visibility, and lanterns may not project light as effectively over long distances compared to flares.