Halcyon's series of Diver Alert Markers provide maximum visibility and redundant flotation at the surface. Open water divers should always carry a marker buoy they can send up in the event of separation from buddy, primary group, or boat. Halcyon Diver Alert Markers feature closed-circuit (one-way valve) construction Inflate at the surface to attract attention Inflate at depth to send up as a surface marker All markers are small enough when deflated to fit in a Halcyon thigh pocket or MC Storage Pak