Scan Visor
The Scan Visor is one of the two visors that Samus will normally have equipped by default in the Prime games. It allows for Samus to scan specific points of interest, including switches which are activated by scanning them, such as the scan post the activates the second set of targets in Exterior Docking Hangar. Most rooms in the Prime games will have at least a couple scan points. Pressing A or D-pad Up will change back to the Combat Visor.
While the Scan Visor is normally not considered a collectable item, certain randomizers have the ability to make it into an item. This will make it so that Samus will not have the Scan Visor by default.
Metroid Prime
In Prime 1, the Scan Visor works by locking on to preset points on the map. Enemies will have these points affixed to them so that Samus can scan them as they are moving. The scans are color coded: red scan points are typically more important for the lore, while orange scan points are not as important. The scan points will become translucent when fully scanned.
Metroid Prime 2: Echoes
The way the Scan Visor works was changed in Echoes. Instead of locking on to preset points, every object that is scannable will be highlighted in the Scan Visor. The color coding was also changed from Prime 1, with red objects being important scans and blue scans being not as important. Once something is scanned, it turns green.
Since the Scan Visor was changed, a number of unintentional quirks were added as a result.
Out of Range Scans
The game calculates if a scan is in range by calculating it based on Samus' line of sight. However, this line of sight doesn't always match with what the Scan Visor is focused on. If the game calculates that something is blocking Samus' line of sight, but she is able to scan it anyway, this results in being able to scan it at ranges otherwise not possible.
Sudden Angle Change
This is another bug relating to how the game calculates Samus' line of sight. In certain cases, such as if a scan is attempted where the scannable point meets with an obstacle that blocks Samus' scan, Samus' facing angle will harshly change to a completely different direction. Sometimes this results in Samus scanning an entirely different scan point.
Metroid Prime 3: Corruption
TODO