The IR Scanner is an item in Perfect Dark.
Generally the only time you will use it is towards the start of Deep Sea when fighting those cloaked guards. As it restricts your field of vision massively you should turn it off right afterwards.
The IR Scanner is also used to find a weak wall in Ruins which you completely circumvent when doing a speed run, and hence useless here.
The IR Scanner is also the subject of a gadget training mission.
|Perfect Dark gadget training|
|Data Uplink | ECM Mine | CamSpy | Night Vision | Door Decoder | R-Tracker | IR Scanner | X-Ray Scanner | Disguise | Cloaking Device|