Sharkbanz 2.0 Shark Deterrent Band is a device aimed at reducing risk when spearfishing around predatory sharks with the use of magnets that don't require charging. Sharkbanz do this by temporarily interfering with their magnetoreception mechanism that sharks (and other fishes of the Elasmobranch Sub-Class) use to navigate the seas. Footage of these deterrents in the water shows their high level of efficacy, especially in dirty water and close proximity. The functional idea is that sharks can experience the same sensory-overload that humans can experience from loud music or bright lights. It seems simple, and chucking a big ol magnet in a waterproof watch housing is how they've done it, so really, it is quite simple. Bear in mind that you're carrying around a big magnet that will affect things as per a standard magnet, so keep it away from any device with magnetic storage - so things like credit cards, disk drives. Lets address the elephant in the room: do these work? There's plenty of research to suggest it works and they've got a tonne of videos suggesting that - so if you believe in science and the scientific method then you know these work.