Some shark repellents work, but none are foolproof. The best-performing personal devices, which use electric fields, reduce the chance of a shark bite by roughly 50 to 70 percent depending on the species and product design. Magnetic bands, chemical repellents, and sound-based deterrents have far less evidence behind them, and some show no measurable effect at all on the species most likely to bite humans.
How Sharks Detect You (and How Repellents Exploit That)
Sharks have specialized sensory organs, tiny gel-filled pores clustered around their snout, that detect electrical fields in the water. These organs are sensitive enough to pick up voltages below 0.05 microvolts per centimeter, which is how sharks locate prey hidden under sand or in murky water. Every living creature generates a faint bioelectric field, and sharks read those signals like a map.
Most shark repellents try to overwhelm this electrical sense. The idea is simple: blast the shark’s sensors with a signal strong enough to cause discomfort, the way a sudden bright light might make you flinch and turn away. The challenge is that different shark species have wildly different numbers of these sensory pores, which changes how they respond. Bull sharks have about 1,850 pores, while white sharks and tiger sharks each have roughly 800. More pores doesn’t always mean more sensitivity to a deterrent, though. The relationship between pore count and avoidance behavior is complicated, and it varies from species to species.
Electric Deterrents: The Strongest Option
Electric shark deterrents are the most studied and most effective personal devices available. These products use electrodes attached to a surfboard or dive gear to generate a pulsing electric field in the surrounding water. A 2024 study published in Scientific Reports tested one surf-mounted device against bull, tiger, and white sharks and found it reduced the probability of a bite by 54% across all three species. A dive-oriented version of the same technology cut tiger shark bites by 69%, though it had essentially no effect on white sharks in that configuration, likely because the electrodes sat too far from the bait to create a strong enough field.
The protective range of these devices is limited. Testing at Flinders University found that personal electric deterrents protect an area within about 3 meters, which is roughly the length of a car. Beyond that radius, the electric field weakens too much to bother the shark. White sharks reacted to the field at about 1.5 meters, while bull sharks didn’t change course until they were just 40 to 50 centimeters away. That’s less than arm’s length.
The voltage needed to trigger avoidance also varies by species. Bull sharks respond at field strengths as low as 3 volts per meter, while scalloped hammerheads require around 18.5 volts per meter. White sharks fall somewhere in between at about 15.7 volts per meter. This means a single device can’t be equally effective against every species you might encounter.
Magnetic Bands: Minimal Protection
Products like Sharkbanz use permanent magnets to create a static magnetic field that, in theory, overwhelms a shark’s electrical sense at close range. Lab studies have shown that magnets can trigger avoidance in several species, including bull sharks, lemon sharks, hammerheads, and reef sharks. In those experiments, however, sharks typically didn’t react until they were within half a meter of the magnet, and their avoidance behavior weakened when they were motivated by food.
When researchers tested magnetic products specifically on white sharks in realistic surfing conditions, the results were discouraging. White sharks interacted with bait 94% of the time when a magnetic band was present, compared to 96% during control trials with no deterrent at all. That’s no meaningful difference. The study’s authors concluded that permanent magnets are unlikely to work as personal deterrents because their effective range is simply too small, unless far stronger magnets or many magnets spread across a surfboard could be used.
Chemical Repellents: Dramatic but Short-Lived
The idea of a chemical shark repellent dates back to World War II, when the U.S. military developed a product called Shark Chaser based on compounds found in decomposing shark tissue. Modern versions use what researchers call a “necromone,” essentially the smell of a dead shark, to trigger an alarm response.
In field tests conducted over five years in the Bahamas, a commercially produced necromone made from putrefied shark tissue caused a dramatic reaction. Feeding sharks halted their behavior within one minute of exposure and temporarily evacuated the area, even with food still present. Chemical analysis revealed the active ingredients are a complex mix of amino acids and organic acids produced during decomposition.
The practical problem is duration. Chemical repellents disperse quickly in open water, making them impractical for long surf sessions or dives. They work in a concentrated burst, not as sustained protection. Researchers have not yet isolated the single active compound responsible for the alarm response, which limits the ability to create longer-lasting formulations.
Sound-Based Deterrents
Underwater speakers have shown some ability to change shark behavior. When artificial sounds were played near baited camera rigs, reef and coastal sharks were less numerous in the area, approached less often, and displayed less investigative behavior. Earlier research found that sudden loud sounds between 150 and 600 Hz caused silky and oceanic whitetip sharks to withdraw.
White sharks, however, are more stubborn. They spent less time near bait rigs when artificial sounds played, but showed no significant response to recorded orca calls. That’s notable because orcas are one of the few natural predators of white sharks, and some companies have marketed orca-sound devices as deterrents. The research doesn’t support that claim.
Why No Repellent Is a Guarantee
Every repellent tested so far has the same fundamental limitation: effectiveness depends on the species, the shark’s motivation, and the distance at which the encounter happens. A hungry shark is harder to deter than a curious one. A bull shark responds differently than a white shark. And most personal devices only create a protective zone measured in centimeters to a few meters, which means a fast-moving shark can close that gap before the deterrent has time to work.
Electric deterrents remain the best option for personal protection, with the strongest evidence behind them. But even the top-performing products still allowed bites roughly 40 to 50% of the time in controlled testing. Magnetic bands showed no measurable benefit against white sharks. Chemical repellents work but fade too quickly. Sound deterrents reduce shark activity in an area but aren’t packaged as personal wearable devices.
For surfers and divers in areas with known shark activity, an electric deterrent meaningfully lowers your risk. It does not eliminate it. Treating any of these products as a guarantee of safety would be a mistake, but as one layer of risk reduction alongside situational awareness, the electric options have real science behind them.