What is Onion Guard? Onion Guard is a knife attachment with a built-in water pump, designed to reduce irritation caused by slicing onions and shallots. These items can produce chemical compounds that cause eye pain and watering when cut. Onion Guard clips onto a standard kitchen knife, and releases water down the blade to neutralize the chemicals that cause eye irritation, making cooking easier. Onion Guard features a built-in reservoir that sits along the top of the knife, a silicone pump button that releases water as needed, and internal channels that direct the flow along the blade. Onion Guard is easy to attach and remove, and is designed to not interfere with the cutting action.