This is a mode that allows you to see beyond your character's (and most human's) usual scope of vision. It has its origins in the thermal scope and night vision mechanics introduced in the Metal Gear series, which required specific items to be equipped in order to use. A similar mechanic is used with the Lens of Truth in Zelda: Ocarina of Time.
These mechanics were expanded into a detective mode in Condemned: Criminal Origins, and more recent games have since started to adopt this feature. Batman: Arkham Asylum can be credited with bringing much attention to this mechanic in recent times.
Detective Mode is an X-ray type vision mode that can be switched on and off. Some uses for it are letting you see:
- Enemies through walls (and differentiate which ones are armed or not)
- A list of the type of enemies within the room (armed or unarmed)
- The rate of each enemy's heartbeat
- Destructible walls
- Items that can be pick ups and certain things that can be scanned (i.e. finger prints, DNA, etc.)
- Red enemies mean they are armed (white enemies mean they're unarmed)
- Transparent walls with cracks means that the wall is breakable (other by plastic explosives or being pulled down with the Ultra Batclaw, depending on the position)
- The list in the middle-right of the screen is a list of total enemies, then broken down into "Armed" or "Unarmed" categories.
- Information text also pops up depending what Batman is looking at. If he is looking at something that can be perched on, it will be circle and text will display telling the player that it can be used to hide.
- While following a trail (finger prints, DNA, tobacco) the particular pieces of evidence will be highlighted and circled