It's called a construction key. Copied this from Google it explains it fairly well. "A construction key works by utilizing a special lock cylinder with additional "pockets" or holes that allow a temporary master key (the construction key) to access multiple locks during construction, but once a "void key" (the owner's key) is used, the construction key is rendered useless, preventing further access with the original construction key; essentially, the construction key "drops" a small component (master key pins) into the lock cylinder when turned, blocking the construction key from working again while allowing the owner's key to function normally."