When you're firing a missile (either from a hand-held launcher or from a vehicle), there's this technology that allows you to "lock on" your target so that your missile could reliably chase it. Usually accompanied by crosshairs and the iconic tone of "Beep.... beep.... beep, beep, beep, beeeeeeeeeeeeeeeeeeep". A screen that actually says "Lock On" is optional. The target, if they're aware (whether by looking or by radar), may attempt to do HighSpeedMissileDodge or use their point defense system to get rid of it.

This trope is common both in films and video games that involve fire-and-forget weapon systems. While representation in media may be [[TruthInTelevision more]] or [[RuleOfCool less]] accurate to real life, most of the associated tropes for both the person aiming and the person being targeted have their basis in real world technology.

Subtrope of HomingProjectile; not all homing projectiles need locking-on first. Compare PlayerGuidedMissile, where the launcher is more hands-on on guiding the missile's flight path akin to a high-speed RC plane; i.e it's far from "fire-and-forget".

Not to be confused with CameraLockOn, which is a {{Video Game Trope|s}} about keeping the camera pointed towards an enemy. If this is happening to you in a video game, that's a form of CrosshairAware.


* Almost all ''Anime/{{Macross}}'' series feature a sequence of the protagonist trying to line up a shot. [[MacrossMissileMassacre Or ten]].
* We also see ''Manga/{{Area 88}}'' pilots waiting for the tone before launching missiles.
* Also done in ''Franchise/SentouYouseiYukikaze.'' What separates them from the rest of the trope is that the lock-on tone is taken directly off an F-15J fighter jet from a JASDF airbase for added realism.

[[folder:Films - Live Action]]
* Used in ''Film/ANewHope'' during the Death Star run. Even though they lock on they can't hit the target, until Luke uses TheForce.
** The first shot didn't hit because it wasn't ''actually'' locked on; the beeping merely indicated that the craft had reached the optimum firing position. Same with the targeting system on Darth Vader's custom [=TIE=].
* Used a lot in the many aerial combat sequences in the movie ''Film/TopGun''
* Film/IronMan uses this somewhat, though it doesn't exactly seem to take him long. He is also on the opposing side in ''Film/IronMan2'' when he is chased by War Machine and the Hammer drones.

* Both the locking-on and locked-onto variants are ubiquitous throughout the Franchise/StarWarsExpandedUniverse, especially in books dealing with pilots in some form or another (read: most of them). Notable in that missiles can be fired blind or on a proximity detonator to avoid giving the enemy any warning, but it's very difficult to actually hit anything doing that.
* Occurs repeatedly in Gerald Seymour's ''Literature/InHonorBound'', which is essentially a book-length duel between a Soviet Mi-24 pilot and a British officer wielding a Redeye missile launcher.

[[folder:Tabletop Games]]
* While ''TabletopGame/{{BattleTech}}'' fiction occasionally mentions this happening (and not necessarily just for missiles -- "lock-on" tones for ''lasers'' have been described before), a special case exists in the actual board game in the form of Streak missiles, which will not even launch unless they get a lock. A failed to-hit roll with a Streak launcher simply results in no missiles actually being fired from that launcher that turn at all, both conserving ammunition and preventing needless heat buildup. They're also virtually guaranteed to hit with the entire salvo if they do launch; anti-missile systems can still take down a few and sometimes a missile will expend itself against partial cover, but no roll on the cluster table is required in and of itself.

[[folder:Video Games]]
* ''Franchise/MetalGear''
** Stinger missiles feature in most of the games and feature the traditional lock-on behavior, with potential targets being marked with a diamond that the crosshairs must be aimed at until it turns red to indicate a lock on.
** For both the first two ''VideoGame/MetalGearSolid'' games, you get the Stinger in order to fight flying bosses or the eponymous HumongousMecha. Of course, you can [[NoKillLikeOverkill use them on regular guards]] if you're feeling so inclined.
*** Both games have Stinger specific missions in the VR training add-on missions.
** Averted in ''VideoGame/MetalGearSolid3SnakeEater'' as the game is set in the 1960's and so the only launcher is the dumb-fired RPG-7.
** The Stinger returns in ''VideoGame/MetalGearSolid4GunsOfThePatriots'' as well as the Javelin, although that functions with fly-by-wire manual aiming to differentiate it functionally from the Stinger.
* In ''VideoGame/GhostSquad'', the boss fight against the helicopter in the Mansion mission equips the player with rocket launchers. Each player has a crosshair that will slowly converge on the target the longer it's aimed at, together with the usual rising beeps and lock-on prompt.
* The ''VideoGame/ModernWarfare'' games both feature missile launchers in both the single player and multiplayer modes. The Javelin includes a targeting screen that highlights potential targets with green boxed that turn red when locked onto. The AT4 and Stinger missiles have no screen, and use only the lock-on tone to indicate when a target is being acquired and then locked onto. The RPG is dumb-fire only.
** For the other end of things, when you are controlling the [=AC-130=] killstreak in multiplayer, you will hear the lock-on warning when you're being fired upon by missile-wielding enemy.
* The move Lock-On in [[Franchise/{{Pokemon}} Pokémon]] is based off of this, enabling the user to (usually) guarantee a hit on the next turn.
* The ''VideoGame/WingCommander'' series used this a lot. Heat-seekers could only lock on if you were behind the target, whereas with Image-Recognition missiles you just had to point at the target for long enough. Torpedoes were an interesting case; they were anti-capital ship missiles that took a very long time to lock on, even though capital ships were very slow moving and couldn't dodge. The explanation was that the torpedo had to synchronize with the enemy ship's shields in order to [[BarrierBustingBlow punch through.]] ''Wing Commander: Prophecy'' further complicated things by requiring the torpedo to target and strike a specific weak spot, such as the engines.
* A staple of the ''VideoGame/AceCombat'' series.
** Being a western-made, Tom Clancy-verse based clone of ''Ace Combat'', VideoGame/{{HAWX}} has it too.
* Very common in the ''VideoGame/ColonyWars'' series, and you also have countermeasure beacons when you're the target of enemy missiles, although the reaction time to use them is punishingly low.
* The ''VideoGame/NavalOps'' series uses this for ship-launched missiles. An AEGIS system allows you to lock on to multiple targets.
* ''VideoGame/GrandTheftAutoSanAndreas'' has this feature, ColorCodedForYourConvenience, on the handheld Stinger missile, the Hydra V/STOL jet fighter and the Hunter attack helicopter.
* ''Franchise/{{Halo}}'':
** ''VideoGame/{{Halo 2}}'''s Rocket Launcher, though it only worked on vehicles. It was [[{{Nerf}} discontinued]] for ''VideoGame/{{Halo 3}}'', and games from ''VideoGame/HaloReach'' onward have it only work on air vehicles (except for a few ''[[VideoGame/Halo5Guardians Halo 5]]'' versions which can also lock on to ground targets).
** ''VideoGame/HaloReach'' introduced the Plasma Launcher, which does have this for all targets. The Sabre fighter also uses it, but since that took place in space, you never find out if it could lock on to terrestrial targets...
** ''2''[='s=] Rocket Launcher also had a slightly peculiar lock-on mechanism in so far as you didn't have to keep your target in your reticle. In fact, you didn't even need a line of sight - you only needed to have the target in your reticle when you started holding down the right trigger, which would start the lock-on process. This means that you could hide behind a large rock, pop out for a split second to start the lock-on, go back behind the rock (breaking line-of-sight to the target), wait the 2 seconds until lock-on was completed, and finally release the right trigger to fire the rocket. Combined with the rocket's very small turning radius, this means that you didn't have to pop out from behind the rock to launch the rocket; looking straight up was enough for the rocket to hit the target even if it was pretty close already.
** The various rocket/missile pods/turrets also usually have lock-on capability, though usually only on air targets.
** ''VideoGame/Halo5Guardians'' introduces the Hydra, which fires micro-missiles that can lock on to even infantry.
** In ''VideoGame/{{Halo 4}}'', the Mantis MiniMecha's missiles/rockets can only lock on to air targets, and only in the campaign at that. In ''VideoGame/Halo5Guardians'', the lock-on is also available in multiplayer, and the campaign version can even lock on to multiple ground targets at once. The ONI Mantis in ''5''[='s=] Warzone mode can also lock on to ground targets.
** In most ''Halo'' games, you get an audible warning when someone has locked on to you. ''Halo 5'', with its abundance of guided anti-vehicle weaponry, has removed this feature.
* All guided missiles in ''VideoGame/{{Warhawk}}'' take time to lock on, represented by a shrinking box around the target.
* ''VideoGame/AfterBurner'' has instant lock-on missile (instead of a beep you hear "FIRE!") Move the cursor over an enemy, launch. Repeat.
* ''VideoGame/ResidentEvil5'' has the LRT laser guided system. The launcher itself doesn't actually do anything, however targeting the boss it is used against long enough results in a converging crosshair and a beep when lock on is made. Pulling the trigger result in a space satellite firing a powerful condensed beam into the boss.
* Rockets and normal torpedoes in ''[[VideoGame/StarWarsBattlefront Battlefront 2]]'' take some time to acquire target lock, but [[GameBreaker homing missiles]] have an instant lock-on.
* In most of the ''VideoGame/StarFox'' series Arwings and Landmaster tanks can lock on and fire homing bombs and charged laser blasts.
* The homing missiles in the ''VideoGame/{{Descent}}'' series make a distinctive sound to their target as they home in. Just one pulse of that sound is enough to make most veterans of the game twitch their fingers to instinctively dodge. Even worse in Descent 3's multiplayer, where players could assign pre-recorded audio taunts to keys. Guess how many people made one of their sounds the homing missile lock-on noise?
* ''VideoGame/FreeSpace'' had this with Aspect-seeking missiles. And [[BigBulkyBomb bombs]].
* In ''VideoGame/LeagueOfLegends'' Urgot's Acid Hunter blades normally fire straight forward, but if someone's been struck with his acid they home in on them. Catelyn's ultimate is a sniper shot that can't miss one she's started lining it up, but can be [[TakingTheBullet intercepted by another champion.]]
* ''VideoGame/ArmoredCore'' series does this too with their missile weapons. This continues until Armored Core 4 where missile lock is indicated by a visual cue, without the beeping.
* In the ''Videogame/MechWarrior'' series, guided missiles require a couple seconds to lock on, at which point they will track an enemy until they hit or run out of fuel. ''Mechwarrior Living Legends'' accompanies it with a [[MostAnnoyingSound constant BEEP BEEP BEEP]] siren when hostile missiles are inbound with your radar engaged. Using the [[TargetSpotter Target Acquisition Gear]] allows for stealth missile attacks, as the TAG laser is invisible to the visual spectrum and doesn't give lock warnings.
** One curious use was a weapon called the NARC Beacon. On its own, it does no damage, it just sticks on the enemy's mech if you hit. However, once it's active, it automatically directs all of your (and your allies') subsequent missiles towards the target unless they're explicitly locked to a different foe.
* ''Videogame/BattleZone1998'' and its sequels have a wide variety of flavors for lock-on missiles; some given lock-on tones to the user, but enemies never hear a warning. In both games, TAG missiles fire a tracer dart, then MacrossMissileMassacre, Shadowers/Comets/Hornets use visual/radar/infrared targeting (respectively) to lock on and then fire. In the sequel, Fire-And-Forget and Swarm (combat) missiles go for the first they detect after being dumbfired, while Swarm (assault) missiles sequentially lock missiles and fire them in succession; from a single rocket to MacrossMissileMassacre. It's possible for NSDF, ISDF, and CCA units to avoid certain locked missiles if they have the proper stealth system fitted on their tank, though Scions have to suck it up and tank the damage.
* In the original ''Videogame/PlanetSide'', the Terran Republic's empire specific anti-vehicle weapon could lock onto targets, but the crosshair had to remain on the target or the missiles would lose the signal. In the sequel, all factions have access to generic anti-vehicle, anti-air, and combined rocket launchers that require a variable amount of time to lock (based on distance) but are fire-and-forget and can only be avoided with flares or some radical evasive actions. The TR Striker and NS Coyote missiles are completely fire-and-forget; simply spray wildly in the direction of a target and the missiles will [[RoboTeching robotech]] into anything that gets in their detection radius.
* The ''Franchise/{{Unreal}}'' series has had by tradition a lock-on function on the rocket launcher, activated when the user holds the crosshair on the enemy for at least one full second. Better yet, the launchers in the series can load up multiple rounds (up to ''six''), for a person-scale {{Roboteching}} MacrossMissileMassacre.

[[folder:Truth In Television]]
* For varying types of targeting systems and varying types of missiles, this can be true to varying extents. A rather bad offender of the "Dramatic Lock-On Delay" was the [[TheScrappy AIM-4 Falcon]], an air-to-air missile carried by US Air Force jets in the 1950's and early 1960's. This missile required the pilot to keep the nose aimed at the target for as long as seven seconds... against ''[[NintendoHard fast maneuvering supersonic fighters]]'', and due to the missiles requiring the tracker head being cooled with a limited supply of liquid nitrogen, if you failed to get the lock on the first attempt, the missile was ''rendered useless''. Only five air-to-air kills were ever achieved with this weapon during nearly two decades of service, including two years of frontline service in Vietnam.
* For some aircraft, such as the C-130J Hercules, the characteristic beeping that warns of a missile lock-on comes from a radio pulse detector. Slow beeps indicate a "scan", usually from a stationary radar installation sweeping over you as it turns; rapid beeps indicate "tracking", where the radar on board another plane attempts to pinpoint you, while the continuous tone, indicating "lock", is due to the radar pointing straight at you. Unfortunately, some modern air-to-air missiles only require the aggressor to achieve the "tracking" stage for it to find you, meaning you may already be dead meat even though the continuous tone hasn't yet sounded.
* There are times where aircraft (or ships, or whatever have you) from two unfriendly nations encounter each other, but don't want to ''fight'' each other. One might be testing the other to see if they will take a stand, or they might be trying to intentionally [[SchmuckBait bait them into starting a confrontation]]. There are various threatening maneuvers that can be done to try and convince the other guy to blink first[[note]]such aggressive maneuvering lead to a mid-air collision and the death of a Chinese fighter pilot in the [[http://en.wikipedia.org/wiki/Hainan_Island_incident Hainan Island Incident]][[/note]], but the generally-accepted be-all-end-all is to attain a missile lock [[IfIWantedYouDead and hold it without firing on the target]], signaling to them that you have them dead-to-rights if they don't disengage. From time to time you will hear about US Navy pilots doing this to aircraft from various other countries which try to get too close to their [[MotherShip aircraft carrier.]]
** This is also used in training exercises and war games with pretty much the same meaning. Often the planes/ships/submarines aren't equipped with missiles or torpedoes, but the lock-on indicates that if they ''were'' they could take down their opponent.
* The lock-on tone for the American AIM-9 Sidewinder series of air to air missiles isn't a beep, but a [[https://www.youtube.com/watch?v=Z_RjqWinRLQ growling-razor type of sound.]] The louder, and more constant the growl, the more solid the lock. Coupled with "SHOOT!" that appears on a pilot's HUD this is an indication that the pilot has achieved weapons perimeters, can safely launch his missile, and guarantee a hit/kill.