RoboCop Versus The Terminator/Secrets

Developers' room: Invincibility
Enable TurboCop cheat mode by pausing the game and pressing: (a sound effect will play as confirmation). Then go to the very left edge of the level, and jump as high as possible while holding. You will enter a room with a photo of the developers, and be granted invincibility for the rest of the game.

Developers' room: Extra lives
Reach the top of a multi-level building with two enemies and a gun pickup on the roof. Jump as far left as possible from the left edge, and you should land on an invisible platform. Jump left again to be bounced up to a final platform (this one visible). Press  to enter a secret room with extra life pickups and a photo of the developers.