The Mares Magnetic Shaker is a magnetic system which makes it the ideal tool for getting heard only when you need. The design is that the ball bearing inside the shaker will stay on the magnet that has been placed at the ends of the shaker inside. Only when you shake it, will the ball bearing move, creating a loud echo sound that will easily be heard by your underwater buddy. It is a useful scuba diving tool and a safety device that most divers should have. Trying to get your buddy’s attention underwater when you can not shout for them can sometimes be a hard thing to do, with the Mares Shaker, this is easy. Due to the fact that the ball bearing attracted to the internal magnet, it will not make any sound until your shake it so there will be no unnecessary noise other wise. This can be connected to your BCD via a D-ring, or you can keep this in your pocket as it is small enough to fit in.