Rainbow Six Wiki

"A thermal scope attachment allows you to see through solid objects such as walls and doors. This vision mode only works when zoomed in and displays "heat signatures" of objects in the world. To activate this vision mode, press the Secondary Fire/Toggle Weapon Attachment key."
— In-game Description

The Thermal Scope is a optical attachment featured in Tom Clancy's Rainbow Six 3: Raven Shield.

The scope allows users to see the heat signatues of enemies when aiming down-to-sights. Additionally, these heat signatures can be seen throigh solid objects such as doors and walls.