WASP Injector Knife

Nobody wants to engage in hand-to-hand combat with a dangerous marine predator. These situations, as uncommon as they may be, can occur. Until now, the diver has been extremely vulnerable and defenseless.

The WASP Injection Knife gives you the ability to defend yourself with deadly force and, if nothing else, it gives you peace of mind and increased comfort while reducing diver stress levels.

When you are crawling around inside a shipwreck with your whole world illuminated only as far as your dive light will allow it is nice to know that you are carrying a weapon that can truly protect you.

As divers, we all know what the effects of compressed gas are underwater. Our training teaches us that our lungs would burst from over-inflation if we held our breath and rose to the surface. This principle is key to the effectiveness of the WASP Injection System.

This weapon injects a freezing cold ball of compressed gas, approximately the size of a basketball, at 800psi nearly instantly. The effects of this injection will drop many of the world's largest land predators. The effects of the compressed gas not only cause over-inflation during ascent when used underwater, but also freezes all tissues and organs surrounding the point of injection on land or at sea. When used underwater, the injected gas carries the predator to the surface BEFORE blood is released into the water. Thus giving the diver added protection by diverting other potential predators to the surface.

Price: $379.95
More information in WASP

I think that it's too much dangerous, there are a lot of crazy people that can use for evil things. Here you can see a video demostration.