Weapon lock is a system that alerts the user of a guided projectile weapon that automatic tracking of a target vehicle has been acquired, and that the fired round will follow the target to the best of its ability.
In the modern- and future-era Battlefield games, all vehicles except light ground transports and non-combat vehicles (such as the Skid Loader) have some sort of warning system that detects the use of guided weaponry. The system uses a visual indicator and an audible klaxon.
The lock alarm does not actually warn against the projectiles used, but rather that an enemy is aiming an AV weapon towards it. There is also no indication of where the offending launcher is located. Anti-vehicle infantry can thus spoof vehicle operators by merely aiming at them (even with empty AV weapons), causing them to waste countermeasures or even leave the area to avoid conflict. Skillful users can also aim off-axis until their munitions are close to the target, or fire unguided to prematurely end the alarm.
Battlefield: Bad Company 2Edit
The Tracer Dart Gun allows certain weapons to acquire weapon lock. Available targets are marked with a red "four corners" icon. When fully locked, a red square icon (surrounding the corners icon) and range to target appears underneath. The square flashes while lock is being acquired.
Players can make use of heat-seeking weaponry such as AA missiles, the FGM-148 Javelin, and vehicle-mounted guided missiles. They can also use laser designators to mark targets for laser-guided weaponry—the weapon carrier must acquire a separate lock while the designator himself is locked onto the target vehicle. A rising chirp signifies active seeking, with a steady high tone indicating lock.
A red square icon indicates a successful weapon lock. A red lozenge with dot indicates a laser lock when teammates are carrying guided weaponry.
Vehicles can detect both locking systems, identifying it as a low beeping tone that goes solid when fully locked. They can also detect incoming missiles, identified as a level high beeping tone. This allows the operator to use countermeasures such as IR Smoke or flares, or to break the lock using ECM Jammer. A skilled operator can also make use of overhead cover against top-attacking laser ordnance, or lateral cover against heat-seeking weapons.
Equipment and gadgets that can provide laser designation are visible to the target as a red laser (similar to the Laser Sight).
Wire-guided weapons such as the BGM-71 TOW, 9M133 Kornet, or an attack helicopter's TV missile do not trigger an alarm, as they do not rely on weapon lock. However, wire-guided weapons do not travel as fast as other guided weapons.
A redesigned lock icon informs the player how well the lock process is proceeding. A thin square icon marks valid targets. Four corners gradually converge into a crosshair, with an additional "Fire" prompt indicating lock. If the weapon system requires constant lock, a "Hold" prompt appears near the icon for the weapon user.
As in Battlefield 3, a red lozenge and dot icon appears when a laser lock is provided.
The early warning system is improved with the addition of a white, directional "threat marker" that resembles the red marker used when taking damage. This allows the vehicle to better respond to the threat. The same sounds are carried over from Battlefield 3.
As of the beta, laser designators do not give visible indication of its use to the user's target.