https://sharkshield.com/shop/freedom7/
I don't have any interest in the company, besides using it, but for any divers out there, this is the product I am using.
Electrical field that sharks find very uncomfortable due to the receptors in their snouts which they use very effectively for locating prey.
The battery is quite powerful and takes several hours to recharge it. It will zap you good if you lift it out of the water and it touches skin.
I realize there are no guarantees in life, but based on the studies I have read it appears to be effective. There are also people out there who disagree with the findings.