How can a diver communicate with the surface during a dive?

A diver can communicate with the surface during a dive through a built-in communications system in the helmet. This system typically includes a microphone and earphones or speakers, allowing for clear two-way voice communication between the diver and surface personnel. It is essential for the safety and coordination of dive operations, as it enables immediate feedback, instructions, and updates, which are crucial in underwater environments where visual contact may be limited.

The other methods listed, such as hand signals, underwater note-writing, or using a whistle or horn, while potentially useful in certain situations, do not provide the same level of reliability and immediacy as a direct communication system. Hand signals, for example, depend on visibility and the recognition of signals, which can be challenging in murky water. Note-writing might be impractical due to water conditions and time constraints. Whistles or horns would be less effective underwater as sound travels differently, and divers may not hear them well. Thus, the built-in communications system represents the most effective and reliable means of communication during a dive.