Heat Seekers are missiles that track heat sources (typically enemy vehicles). They differ from laser-guided, radar-guided, or wire-guided weaponry.
— Battlelog description
Heat Seekers is an air vehicle specialization featured in Battlefield 3.
Heat Seekers add a secondary weapon designed to counter other air vehicles. It is available for scout helicopters, fighter and attack jets, attack helicopters, and AA Tanks. Upon acquiring weapon lock, the pilot can fire up to two missiles, either the AIM-9L Sidewinder for US, or the R-73 Archer for RU, that will continue to track the target. The missiles also behave in a realistic fashion in that they follow the closest heat source and not always the targeted jet. Examples of this can be seen if a Heat Seeker is shot at two nearby airborne vehicles and the non targeted vehicle flies in the missile's path, causing it to change course and track said vehicle. This can cause unintended results such as a missile meant for a jet tracking a MAV instead. Only the vehicle's pilot may use the weapon. Any airborne vehicle can be targeted, from fighter aircraft all the way down to Micro-UAVs, and everything in-between.
When activated, the pilot's HUD changes to a perforated targeting circle, showing its lock-on area. One can tell if a successful lock-on by a low beeping tone and if the targeting reticle is flashing. A lock-on usually takes 3 seconds to lock, but with the upgrade Beam Scanning, the Lock-on will only take around 1 second. Each missile deals 45 damage to enemy jets, dealing a total of 90 in damage if both of the equipped Heat Seekers connect. Since a jet's disable threshold is 37, one missile hit will not disable the aircraft, but striking with the Main Gun or second Heat Seeker will have it disabled. Heat Seekers can be avoided in multiple ways including IR Flares which distract missiles in flight, ECM Jammer which will prevent lock on for a few seconds when deployed, by leading the missile into a solid object, and by luck in the case of missiles occasional missing their target for a multitude of reasons.
— In-Game description
Heat Seekers are a vehicle Secondary Weapon featured in Battlefield 4.
Like in Battlefield 3, the pilot must obtain weapon lock on suitable target. Much like the FIM-92 Stinger's missiles, Heatseekers automatically track the target, after launch, but may be spoofed by countermeasures and can divert their course if another heat source passes by.
All aircraft, except for the Transport Helicopters, can be equipped with heatseekers and are launched in twos. Mobile AA however can launch up to 4, with 2 per magazine. All deal 40 damage per hit.
Heatseekers are capable of performing Mobility Kills to all types of jets and helicopters but can be diverted by IR flares and ECM Jammers can make it even harder for it to land a hit. Also, they cannot swerve round when the targeted aircraft turns very sharply. Since the Below Radar upgrade, Heatseekers cannot be given targets flying too close to the ground.