Switchblade

A switchblade is a type of knife with a folding or sliding blade contained in the handle which is extended automatically by a spring when a button, lever or switch on the handle or bolster is activated. Most switchblade designs incorporate a locking blade, in which the blade is locked against closure when the blade is extended to the fully opened position. It is unlocked by a mechanism that allows the blade to be folded and locked in the closed position.