IR Smoke

IR Smoke is used by military forces to mask the movement or location of units such as infantry, tanks, aircraft or ships. The smoke provides sufficient screening even in the infrared electromagnetic region, unlike carbon emissions or fog.

Battlefield 3
IR Smoke is a ground vehicle specialization. When used, the driver of a tank or other armored vehicle gains the ability to use smoke launchers on the vehicle, that will obscure both view and thermal imaging. It is deployed by pressing the button.

So long as the vehicle remains in the smoke area, enemy guided weapons will lose weapon lock and miss the vehicle. Unguided weapons still have a chance to strike the vehicle.