The sequel "" was released in 1990 for the MSX2. It further evolved the stealth gameplay of its predecessor and introduced most of the gameplay elements present in "Metal Gear Solid", including the three-dimensional element of height, allowing players to crouch and crawl into hiding spots and air ducts and underneath desks. The player could also distract guards by knocking on surfaces and use a radar to plan ahead. The enemies had improved AI, including a 45-degree field of vision, turning their heads left and right to see diagonally, the detection of various different noises, being able to move from screen to screen (they were limited to a single screen in earlier games), and a three-phase security alarm (where reinforcements are called in to chase the intruder, then remain on the lookout for some time after losing sight of the intruder, and then leave the area). The game also had a complex storyline and improved graphics.