The device is about the size of a mobile phone
The company, called Sea Change Technology, says the device is the result of six years' research in the most shark-infested waters of the world.
The device works by surrounding the swimmer with an electrical field which affects the shark's central nervous system.
The closer the shark gets, the more severe the effect becomes, until at close range, say 2-3 metres, the shark develops spasms and intolerable pain which compel it to turn away.
The device can be fastened around a swimmer's ankle where the makers say it will work for about two hours before the battery needs recharging.
Ecologically friendly
There is a slightly larger version for recreational divers.
Both these tiny devices were developed from research which began in South Africa.
The Australian makers say they are already working on another version to protect whole beaches, enabling authorities to remove the nets and hooks that kill many protected species, including dolphins and turtles.
One advantage of the new technology, they say, is that it affects only sharks. Other marine creatures ignore it.
Jerry Kleeman, managing director of SeaChange, told reporters that the device's electronic field affects the shark's nervous system through sensitive receptors near its snout.
As the shark approaches the discomfort it feels increases, until its muscles begin intolerable spasms.
"It puts out a very precise electrical field that sharks perceive because of a hunting sense they have.
"So as sharks get closer to you they will veer away very rapidly as it becomes uncomfortable for them, but it doesn't cause them any lasting harm. It also does not impact on any other marine creatures or humans," he said.