
Alien Syndrome (set 4, System 16B, unprotected)
Released in 1987 by Sega for its System 16B arcade hardware, Alien Syndrome is a beloved top-down run-and-gun shooter that defined 1980s arcade action. This specific version, the unprotected set 4 build, removes the original encryption locks that limited play on many retro emulators, delivering a smooth, authentic arcade experience without glitches or missing content. The game puts players in control of either Ricky or Mary, two space commandos tasked with infiltrating alien-infested space stations, research outposts, and alien planets to rescue trapped crew members before a countdown timer triggers a deadly explosion that wipes out the entire facility. Each level features sprawling, maze-like layouts teeming with over 20 different alien enemy types, from fast-moving facehugger-style parasites to giant, acid-spitting abominations. After rescuing the required number of crew members marked on your heads-up display, you gain access to the boss chamber, where you face off against enormous,

The emulator loads after you press Start Game.
How to Play Alien Syndrome (set 4, System 16B, unprotected)
Save & Load States
- F2Press F2 to save your current game state at any time.
- F4Press F4 to load your last saved state.
- F3Use F3 to switch between save slots.
Save states are stored locally in your browser. They persist across sessions but are cleared if you clear browser data.
Customize Controls
Click the gear icon on the emulator toolbar → "Controls" to remap keys.
Default layout for ARCADE. Remap in emulator settings.
About Alien Syndrome (set 4, System 16B, unprotected)
Alien Syndrome (set 4, System 16B, unprotected) is a classic ARCADE game you can play online for free in your browser. No download or installation is required — click "Play Now" to start instantly. Relive the experience of vintage console gaming with authentic gameplay, right in your browser on any device.
This title is part of the PLAYERETRO game collection, which features over 1000 classic titles across multiple systems. Use the keyboard controls shown above to move and interact. Save your progress with save states and enjoy Alien Syndrome (set 4, System 16B, unprotected) anytime, anywhere.
Play Alien Syndrome (set 4, System 16B, unprotected), the iconic 1987 Sega arcade run-and-gun shooter, for free online at PLAYERETRO. Fight alien hordes, rescue trapped crew, and defeat massive bosses