What is the main purpose of a surface marker buoy (SMB)?

The main purpose of a surface marker buoy (SMB) is to signal for help. When a diver is underwater and needs assistance or has completed their dive and is surfacing, the SMB is deployed to indicate the diver's location to boats and other surface personnel. This is vital for ensuring the safety of divers, especially in busy waters where boat traffic is present. The buoy floats on the surface and is visible to others, allowing them to be aware of the diver’s position and provide necessary support if needed.

While enhancing visibility is a function of a surface marker buoy, as it does make the diver more noticeable at the surface, the primary and most critical aspect is its role in signaling for help. Storing air and recording depth do not relate to the function of an SMB; those roles pertain to equipment specifically designed for those purposes, such as tanks or dive computers.