An automatic knife or switchblade is a type of knife that comes with a folding or sliding blade contained in the handle. The knife opens automatically by a spring when a switch, button, or lever on the handle is stroked. Most switchblade designs integrate a locking mechanism in which the blade is locked against closure until the spring extends the blade to the fully opened position. The block gets unlocked through the manual operating mechanism and allows it to be folded and locked in the closed position.