The underwater maracas are allerting devices designed to make a rattling noise when shaken. Also known as "shakers".
The Scuboing is an underwater acousting alerting device allowing you to attract the attention of the nearby divers.
Magnetic holder allowing attachment of BestDivers underwater maraca/shaker signalling device to a 20mm hose.
The safety whistle is an inseparable part of every SCUBA or freediver's gear.