Dive knives are essential safety tools used for cutting through entangled lines, nets, or other hazards underwater. They typically feature a serrated edge for cutting through tougher materials and a straight edge for general use. Dive knives come in various designs, including fixed-blade or folding models, and are usually made from rust-resistant materials such as stainless steel or titanium. Proper placement and accessibility are crucial for quick use in emergencies, and regular maintenance is needed to ensure the knife remains sharp and functional.