switchblade
A switchblade (also known as switch knife, automatic knife, pushbutton knife, ejector knife, flick knife, gravity knife, flick blade, or spring knife) is a folding knife with a sliding or pivoting 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. Virtually all switchblades incorporate a locking blade, a means of preventing the blade from being accidentally closed while in the open position. An unlocking mechanism must be activated in order to close the blade for storage.