Retinal scanner

Good

The Retinal Scanner is a device used by the Black Mesa personnel in the Black Mesa Research Facility.

Half-Life and its expansions

 * In Half-Life, Black Mesa scientists and security guards will use them to open to way to the player to restricted areas. Sometimes only one person in available and killing him will prevent the player from proceeding. In that way the player is forced to think and be careful before shooting anything that moves.
 * When idle, the screen is blue. When used, it turns to orange and shows a green circle around a flesh-colored dot. When the access is granted, a beep can be heard. When the access is denied, a voice says "Access denied".
 * After the Resonance Cascade, many Retinal Scanners are broken, preventing the player to use the nearby door or forcing them to break the door window.
 * In Blue Shift, Barney and Rosenberg reach an older part of Black Mesa, when Hand Scanners and different Chargers are used. It is likely they were the primary scanners used in Black Mesa in past, subsequently replaced by Retinal Scanners in the modernized areas of the facility.
 * In Decay, the brush Retinal Scanner was replaced by a detailed model. This shows the actual scanning component on a hinged pivot with the word "SECURITY" on it. The screen, when activated, shows a clockwise circling of a crosshair-like scanner process around an orange retinal image.
 * The beeping sounds of the original version vary. Sometimes briefly, sometimes very long, and either high or low.

Half-Life 2
In Half-Life 2, a Retinal Scanner is operated by Kleiner in his lab to access the teleport. Hidden inside a column, it can be accessed by moving the Black Mesa scientists portrait. It is not seen later, being mostly a nod to the previous episodes.

Behind the scenes
The Security Card was originally to fill that role but was cut in favor of the Retinal Scanner, forcing the player to preserve lives instead of picking a security card on a corpse.

List of appearances

 * Half-Life: Day One
 * Half-Life
 * Half-Life: Opposing Force
 * Half-Life: Blue Shift
 * Half-Life: Decay
 * Half-Life 2