Boss Warning Siren

In case the ominous, interlocking double doors you took to get in here weren't enough of a clue.

"WARNING! A HUGE BATTLESHIP 'KING FOSSIL' IS APPROACHING FAST."

— Darius

In some video games, before you fight a boss, the screen will start flashing red while the word WARNING! flashes up on the screen as the stage music fades out or stops abruptly. Sometimes, it could be a visual warning or an audio warning; it doesn't necessarily have to be both. In any case, this lets the player know that a more powerful foe is imminent.

Often a Most Wonderful Sound, especially if it precedes an awesome boss. Though when it precedes That One Boss, it also means "This Is Gonna Suck."

May overlap with Boss Subtitles. Related to Fight Woosh and Red Alert. See also Suspicious Video-Game Generosity.

---

Examples:

Action Adventure

• Played with in Axiom Verge, where the track used for Uruku, the hallucination boss, and the Final Boss starts with an air raid siren.
• Blaster Master:
  • The NES game has boss rooms that do this without the text message. The screen begins to repeatedly flash as an alert siren stops the music, before fading out the screen completely and revealing the boss. Interestingly, you can still leave the room just before the screen fades out completely, allowing you to go back and better prepare yourself if you're not ready to fight them.
  • Warnings also appear in Blaster Master Zero, with added Boss Subtitles. Unlike the NES game, however, the room doesn't darken, and you don't have an opportunity to quickly retreat. In-universe, this is a feature of the Metal Attacker's AI; this is why Jason himself is assigned the title "Blaster Master" by Kane's MA.
• Golden Force throws one of these before an incoming boss fight, in the form of bright red bars with the words WARNING! written in caps.
• The Guardian Legend uses warning sirens in both the flying and ground stages just before a boss battle starts. On the ground, you can leave the boss arena just before the pyramids seal off all of the exits.
• Once you unlock a boss in La-Mulana and have at least one Ankh Jewel, the track "Requiem" plays when you're in the room with the boss Ankh. Additionally, every boss theme starts with the same Recurring Riff.
• NieR: Automata has a warning card accompanied by a klaxon whenever a Goliath class machine is detected. These range from machines the size of a house to machines the size of a skyscraper. This siren also plays during important boss fights.
• In Assassin's Creed Origins whenever one of the powerful Phylake warriors gets within 100 metres a war horn blasts. Since they move freely within a certain area of the world and are often far more powerful than you probably are at that time, it's incredibly helpful. Even better, if you do fight and defeat one, the war horn sounds again this time sounding a bit strangled and defeated putting that sweet end note to a good fight.
• Each boss fight in Vernal Edge is prefaced by a screen displaying the boss's name alongside a progress bar that becomes their health bar when it's finished loading ^note it's possible to land a few hits and even get off a charged attack or two before this with two scrolling marquees on the top and bottom of the screen reciting the poem "Fire and Ice" by Robert Frost.

Action

• In Boneraiser Minions, King Gigald's entrance is announced with flashing text followed by trumpet fanfare as he makes his entrance at the end of a normal run. For Castle Conquest mode, Queen Gigalicious doesn't get the text, but does get the trumpet fanfare and gives an Evil Laugh.
  King Gigald thirsts for thy head!

Beat 'em Up

• Played with in the remixed boss theme from Streets of Rage Remake, which begins with a sample that sounds like a siren.
• In Bayonetta, level 14 has the music stop and a siren resounding just before you fight Mini Bosses Courage and Temperance. Comes along with this entire Shoot 'Em Up section being a homage to After Burner.
• Eight Man (1991) throws a "Warning!" screen before each boss stage, with the boss looking menacingly at the player as the red background blinks rapidly. You have two seconds to prepare for battle.
• Jitsu Squad will let out a huge "DANGER!◊" prior to boss fights.
• The Wonderful 101 adds an alarm tone and a "WARNING" pop-up on the Mook Debut Cutscene for bosses. In addition, Operation 006-A's miniboss (being an Unexpected Shmup Level) features the same pop-up before the boss without the debut cutscene.
• Dadgame has a large warning appear on screen before facing Final Weapon or Final Weapon X. This has the added benefit of highlighting where the boss will be appearing, because otherwise it would be possible to get accidentally caught under its feet just as it comes out.
• Ninja Baseball Batman always starts the fight with some baseballs popping out from underground and blowing a fanfare on their trumpets to herald the incoming boss.
• Yakuza 0 has the Mr. Shakedown enemies, who's theme music begins with a warning siren. Reign, the track that plays while Majima storms the Dojima Family's HQ, also starts with a siren - except you're the boss.

Driving

• In Buck Up And Drive!, when a police car shows up to assault you, a police siren plays and the filled-up Heat gauge is replaced with "IT'S THE POLICE!" (Or a slang term in place of "police", such as "rozzers", "law", "bobbies", or "plods")

Fighting

• Super Smash Bros.:
  • The series generally has a klaxon of some sort for Bonus Character battles.
  • In the Wily Castle stage in Super Smash Bros. for Nintendo 3DS / Wii U, a faint warning siren can be heard before the Yellow Devil makes its appearance.
• The Mega Man Zero example below also carries over to SNK vs. Capcom: SVC Chaos, where the klaxons sound whenever Zero is about to confront any of the bosses, including Shin Akuma and Serious Mr. Karate, in the boss battles, but not against any normally playable characters.
• In Capcom vs. SNK 2: Mark of the Millennium, if you meet the requirements for one of the two midbosses:
  Announcer: "This is the final! This is wh—Wait a second! A new opponent has interrupted the tournament!"
• Once the Gundam Vs Series starts adding in Mobile Armors as bosses, the pre-fight screen signifies a boss stage with a warning klaxon, often accompanied by the words "ENGAGE UNKNOWN ENEMY". Starting with Extreme Vs., your Navigator will also start to get uneasy when you select a boss stage.
• Most bosses in the Virtual-ON series are accompanied by one. The first game had "WARNING" flashing on the screen accompanied with a siren when facing the mid-game penalty boss, while later games would have the word cryptically being said out loud by the announcer. In all of these instances, the sirens or the word is heard four times before the boss appears.

First Person Shooter

• In Blake Stone, a warning klaxon or similar signal normally sounds just before the Final Boss Battle in each of the six missions.
• Overload features a loud siren and a menacing message about a massive incoming threat as the player enters the boss area.
• Primal Carnage: If the human team captures the penultimate checkpoint in the Get to the Chopper game-mode, the distant roar of a Tyrannosaurus will thunder over the map. This signals to all players that Tyrant class dinosaurs are now unlocked for the dinosaur team.

MMORPG

• In Elsword, every boss had one before the boss fight starts.
• In MapleStory, the appearance of an Elite Boss (a unique boss that gives special drops) has a loud siren proceeding it on the current and a message flashing on every map in the zone, letting all players there know about it.

Miscellaneous Games

• All WarioWare titles have a sound clip whenever a boss stage is coming up next and will linger on the screen between microgames eight beats longer than normal. There will usually (but not always) be an on-screen message telling you that you're about to encounter the boss. Said sound clip varies from game to game, but that in WarioWare: Smooth Moves sounds particularly like a klaxon played to a beat.
• Trash Panic has a warning siren with a red hue and big letters overtaking the screen right before a "boss" trash piece comes up for you to dispose. Unlike some other games, the huge alert signs are necessary, since it's the biggest piece of trash, you have a set amount of time to break it down (you get a HUGE penalty if you do not), you can't "hold" it, and it's usually very sturdy. The player NEEDS to know when this comes in, thus the sirens and redness.
• Inverted in Descent I and II, where an escape warning siren sounds after each boss is defeated... because the boss is usually a Reactor Boss that, by damaging, you just triggered a nuclear meltdown.
• Downplayed in Terraria. When bosses occur naturally they are accompanied by an onscreen message (such as "You feel an evil presence watching you" for the Eye of Cthulhu, or "You feel a quaking deep underground" for the Destroyer) each boss having a unique message so the player can tell which one is coming. When summoned a message saying "(Boss Name Here) has awoken!" accompanied by a common boss monster roar. In addition to an onscreen message, the screen blurs and darkens and the music fades to silence when the Moon Lord is about to appear.
• Before fighting a boss in Crash Fever a siren will sound out along with the message “Area Boss Appeared!!”.
• Used in Jetpack Joyride 2 after you get a required amount of score before fighting a boss. A pop-up in angle brackets is yellow if it's a King Mook version of a regular enemy or The Science Crew, and red when it's the leader of the laboratory you're in. They and The Science Crew also get separate banner displaying their name.

Platformer

• In The Angry Video Game Nerd Adventures, the "Boo! Haunted House" stage parodies A Nightmare on Elm Street (NES) with the warning BIMMY'S©™ COMING!.
• Bubble Bobble: Occurs with the battleship Yamato in Bubble Symphony much like in Darius, and with each boss in Bubble Memories.
• Catherine: "_____ has appeared. It's the killer. Do not die."
• COGEN: Sword of Rewind: Every boss is prefaced with a red-on-black "WARNING" across the screen, as well as blaring alarm, while their health bar fills up.
• In Donkey Kong Jungle Beat, after levels before a boss appears, if it is the banana eating minigame and then after clearing that, there will also be a sound to signify a boss is approaching. The Kong bosses give out an Evil Laugh, the hog bosses give out a laugh that sounds like they are Laughing Mad, the roc bosses give out a screech, and the tusk bosses give out an mechanical elephant sound. During that sound, the monkeys run off and Donkey Kong turns to face the silhouetted boss.
• Perhaps the weirdest boss warning comes from the PS1 game Eggs of Steel, where a cutscene plays before certain bosses showing the game's Big Bad dancing and challenging the player to "BEAT MY BOSS!".
• Giana Sisters: Twisted Dreams: It comes accompanied with Boss Subtitles.
• I Wanna Be the Guy, parodying Ikaruga, provides a klaxon and "WARNING: NO REFUGE" sign when Mecha Birdo is approaching.
• In Magical Doropie, Boss Only Levels are herald with a screen saying "ALERT!!" in big letters on a black screen flashing red. The player then appears in the level while the boss makes its entrance. When the boss's entrance is finished, a "Data File" on the boss appears, listing its name, health, strength, speed, damage and special ability. However, in the final stage, none of the final three bosses have any alert screens or data profiles, although the siren is still heard while the final boss is materialising.
• Mega Man:
  • The Mega Man X series has this starting from Mega Man X4, just before the boss appeared on screen and monologued with the player character. It was carried over to the Mega Man Zero and Mega Man ZX series as well, although in those cases it happened just before the fight begins after the boss's monologue.
  • The Mega Man remake Mega Man Powered Up also had this, despite not being present in the other games from the classic series. As this was the Lighter and Softer version of Mega Man, the warning is presented in a colorful non-serif font, and Roll is heard saying "Warning!" in an oddly cheerful voice.
  • Maverick Hunter X added them to a remake of the first Megaman X as well. In both cases, they masked UMD load times much as the ones from X4-X8 masked CD load times.
• Mega Turrican has a klaxon ring and a voice shout "EMERGENCY! EMERGENCY!" when encountering a boss, except for The Machine.
• Metal Storm flashes "RED ALERT!" when the player is about to fight the level boss. Does not apply to the Boss Rush at the end, however.
• In several platform games made by Rare, such as Jet Force Gemini (also an action game), Donkey Kong 64 and Banjo-Tooie, among others, a boss is presented through a lengthy cutscene as onminous music plays. The buildup of the battle may be based on either the boss's slow but climactic arrival to the battle arena, or even the assembling of the boss (as in the case of Mr Patch in Banjo-Tooie and King Kut Out in DK64). Notably, for each of the three mentioned games the background music building up the encounter is the same (including for the Final Boss), whereas in Conker's Bad Fur Day and Star Fox Adventures each boss has its own music presentation.
• In Run Saber, normally an arrow appears at the top of the screen showing you which way to proceed through the stage. However, when a boss is encountered, an ALERT! icon blinks there instead.
• Justified in Sonic Adventure 2's boss fight against the Flying Dog. In the cutscene preceding the battle, Rouge is caught sneaking into a maximum-security vault and triggers an alarm that alerts the boss to her presence.
  Flying Dog: This is Flying Dog to Headquarters. Intruder found in the Security Hall. Preparing to attack.
• In Sonic the Hedgehog 2, the final boss BGM starts with a blaring klaxon.
• In the Sega Genesis Spider-Man video game, Spidey's Spider-Sense always goes off just before a Boss villain appears with a quick visual of the usual wavy lines around his head. However, this is also a signal of a prime opportunity to take a picture of the enemy to sell to the Daily Bugle for more webfluid.
• Valis II: "WARNING: A strong warrior, (Adjective Noun Fred), is coming!"
• VVVVVV has a screen named "The Warning". One conveyor belt tunnel, no spikes, eight checkpoints in a row. Immediately after this screen comes the path to Doing Things The Hard Way, a six-screen long gauntlet of spikes traversed both ways.

Rhythm Game

• BIT.TRIP: All the original six games display the word "BOSS" when confronting one, though it's most prominent in FATE where sound cues accompany the warning.
• DanceDanceRevolution games that feature an Extra Stage will sound an alarm if you meet the requirements for it.
• In beatmania IIDX, after unlocking an Extra Stage boss song, the music select BGM will be overriden by a short loop of the boss, or a new BGM altogether from beatmania IIDX 20 tricoro onwards. In some cases, the background will change accordingly. This only applies to bosses that are made available on the standard music select screen, not bosses accessed through a special "boss select" screen (e.g. beatmania IIDX 13 DistorteD's Cardinal Gate or beatmania IIDX 16 EMPRESS's Empress Place).
• Following two normal tracks in Just Shapes & Beats‘ Challenge Mode, a short guitar riff plays as “WARNING: BOSS BATTLE” appears on screen.

Role Playing Game

• Chrono Trigger features a diegetic version when the party enters a restricted area in the Bad Future, just before the robotic Guardian boss crashes down from above, knocking them all to the ground, and activates its defense routine.
• From Disgaea 2: Cursed Memories onward, whenever a Pirate group is due to arrive in the Item World, the screen will flash red as a siren plays. Disgaea 5: Alliance of Vengeance even has a WARNING flash up on screen. Disgaea Dimension 2 is the only exception, as Pirate Groups tend to appear on the floor at the very beginning of that map.
• Some of the tougher bosses in Limbus Company, such as certain Abnormalities, the Final Boss for each Canto dungeon, and Ricardo will have a special intro before their fight, namely the appearance of a red runic circle and 7-pointed star inlaid with the most well-known phrase from the Divine Comedy.
  PROELIUM FATALE: LASCIATE OGNI SPERANZA, VOI CH'ENTRATE^TranslationFatal Battle: Abandon all hope, ye who enter here
• Shin Megami Tensei I and Shin Megami Tensei II normally avert these—most of the type you're given no advance warning for upcoming bosses. However, if you encounter one of the Fiends, each of which have a 1/256 chance of showing up while their specific requirement is met, the game gives you a warning message, asking you if you want to stand your ground. If you say "yes", the game asks you if you really want to stand your ground. Say "yes" again and the battle immediately begins. This carries over to Shin Megami Tensei IV as well—see below.
• Shin Megami Tensei: Nocturne: "The flames of the Candelabrum of Sovereignty are flickering wildly...." This is your one warning that a Fiend is close by. Get to where they're lying in wait, and you'll get the message "You sense the presence of a terrifying demon.... will you stay here?" Answer yes twice and the battle begins.
• Shin Megami Tensei: Strange Journey:
  • When you're approaching a sector endboss, your Demonica alerts you and pinpoints the location of the boss room. Subverted in Sector Bootes, when you approach Mitra's lair and get this warning, but when you enter, you're simply greeted with a speech and get escorted back to the Red Sprite afterwards. The warning doesn't trigger again when you approach Mitra's room a second time to assault him, but since you now know his location, it's not necessary.
  • Late into the game, in Sector Fornax, your Demonica warns you on multiple occasions that a powerful demon is nearby but cannot pinpoint their coordinates. Proceed further and sure enough, you face the One-Winged Angel form of one of the first four sector bosses.
• Shin Megami Tensei IV:
  • Your Gauntlet's AI, Burroughs, will alert you if there is a boss demon nearby or behind a door.
    "I'm detecting a strong demon ahead. Do you want to go on?"
    "Master, look out. I'm detecting a strong demon nearby."
  • If you encounter a midboss or certain Optional Bosses, Burroughs urges you to "be careful."
  • If you encounter a Fiend, Burroughs urges you to get out, and the same style of "will you stay here" prompts from Shin Megami Tensei I and II will pop up. Say "yes" to both and the battle immediately begins.
• Shin Megami Tensei IV: Apocalypse doesn't have Burroughs to warn you of "strong demons"; instead, the game usually just tells you that "you sense something strong" up ahead. However, you also get the Shesha Radar, which gives you increasingly intense alarms as you get closer and closer to Shesha.
• Undertale: During the final boss of the Neutral Route, Photoshop Flowey, a warning siren will sound before Flowey uses the special attack of one of the six human souls.
  WARNING!
  WARNING!
• Pick a fight with a high-level unique enemy in Xenoblade Chronicles 1, and your party members will spout warnings that seem to be meant just as much for the player as for the party leader. Some examples:
  Shulk: Are you sure this is a good idea?
  Sharla: Are you trying to get us killed?!

Run and Gun

• Commando: Steel Disaster plasters a blood-red "WARNING!" sign over the screen, right before each boss battle.

Shoot' em Up

• The shoot-em-up genre loves this trope. See this compilation video for some of the better-known ones.
• Coryoon has a generic red "WARNING!" before each boss fight. The final stage, a Boss Rush, repeats this and have you seeing a "WARNING!" before each rematch.
• Darius has "A huge battleship is approaching fast!" in most (if not all) of its titles to herald the arrival of its various fish-inspired bosses.
• EXTRAPOWER: Star Resistance: WARNING! HYPER ENERGY COMES SOON!!
• Radiant Silvergun has the entire screen taken over with the word "WARNING", as well as the warning "NO REFUGE" and the memetic "BE ATTITUDE FOR GAINS" before every boss fight.
• Ikaruga, the spritual successor to Radiant Silvergun, had a similar message: "WARNING: The big enemy is approaching at full throttle. According to the data, it is identified as "Butsutekkai". NO REFUGE".
• Sega Master System's Astro Warrior shows a message "Warning! Destroy <Boss Name>" before each boss.
• In Star Fox, almost all boss battles were announced by an alert klaxon and a short voice clip of "incoming enemy". As this was invariably near the end of each level, it occurred while the level music was fading out to be replaced with the boss battle music.
• Warning Forever does this despite being a Boss Only Game, also giving you its name and a brief chart on its weaponry.
• Blazing Star has before a boss battle an alert klaxon and the message "WARNING" as well as different texts with more or less Engrish.
• Indie video game ''Chalk'' has the word "WARNING" flash on screen and an opera singer singing "oooohaaaahAAAAAH!" for its boss siren. The last stage includes the siren at the start of its music, which is appropriate since it's a boss rush.
• Einhänder gives a warning that is themed into the level. For example, in the first level, after fighting your way through the city, the police decide that they can't take you down, so they follow behind and ahead of you like a low speed chase, keeping their sirens going while they basically escort you right towards the first boss. Following bosses might have klaxons sounding off to indicate that the boss is powering up and becoming mechanically operational, or have someone over a PA system order for another boss to scramble and prepare for battle.
• The Thunder Force series:
  • In Thunder Force II, a siren plays when encountering a midboss in a horizontal-scrolling segment. A lower-pitched one plays when facing the stage's endboss.
  • In Thunder Force III, bosses are preceded by a siren and the word "EMERGENCY" scrolling across the bottom of the screen.
  • In Thunder Force IV, a siren sounds when a boss battle is about to begin.
  • In Thunder Force V: "ALERT! The enemy is (approaching fast) / (dead ahead)! Code Name: <boss name> - <boss description>".
  • In Thunder Force VI, you get a siren and your ship's computer alerting of the boss in Tangut, followed by the name and description of the boss, both in English and Mongolian.
• In Heavy Weapon this occurs with the Danger! Danger! in bold letters once you get to the end of the stage. It also shows the boss' weapons and abilities (with the exception of the Final Boss).
  • Finally, an arrow will also point in the direction the boss approaches from- this is important because two of them (Mechworm and X-Bot) will One-Hit Kill you if you stay in the wrong spot where they appear.
• Touhou Chireiden ~ Subterranean Animism: Utsuho Reiuji, the nuclear-powered Hell raven girl (and final boss) of the game, has the distinction of prefixing each of her spell cards with klaxons while the text '☢ Caution !! ☢' flares on-screen.
• In the old arcade game Time Pilot, a loud warning will sound before the boss shows up on any given level.
• In Beat Hazard, a warning sound is played when a boss is about to enter the screen.
• At one point in Fantastic Journey, the player encounters the Moai Battleship, with its placement randomly determined inbetween two of the regular stages. When the player is about to encounter it after clearing one of the stages, its own music theme plays instead of the chosen player character's theme and the message WARNING flashes on the screen.
• Axelay has an audible warning siren when approaching a stage boss.
• RefleX plays an audio siren and displays a "WARNING" banner that displays the name and subtitle of the boss. The siren is also used when ZODIAC Virgo comes out of nowhere in a cutscene to finish off Cancer.
• Judgement Silversword:
  • "WARNING — HERE COMES THE JUDGE! [ <boss name> ]"
  • Changed slightly for the final boss:
    "WARNING — [ JUDGEMENT SILVERSWORD ]"
  • And again for the Final Boss of Special Mode:
    "WARNING — HERE COMES THE FINAL JUDGE! [ E3 ]"
• RayCrisis has "ALERT: GENERATING HUGE ANTIBODY: [boss name]". The PlayStation port interrupts the music with an audible siren during the warning screen. A different alert is used when you return to the Self-Field to fight the Final Boss.
• DonPachi: "WARNING: THIS IS NOT SIMILATION. GET READY TO DESTOROY THE ENEMY. TARGET FOR THE WEAK POINTS OF F**KIN' MACHINE. DO YOUR BEST YOU HAVE EVER DONE." ...And in the sequels: "You are approaching the target of attack. The mission starts now! Are you ready?", "Watch out! Watch out!", and "An unidentified battleship/unprecedented tremendous force is approaching!"
• Dangun Feveron brings us "HEAVEN IS HERE INSIDE MY SOUL!"
• From Hellsinker:
  • AN AWESOME PRAYER IS CONFLICT WITH US — KEEP YOUR DIGNITY
  • NOW REACHES THE FATAL ATTRACTION BE DESCRIBED AS 'HELLSINKER' -- DECIDE DESTINATION
• Triggerheart Exelica: "EMERGENCY. EMERGENCY. Your target is approaching."
• Crimzon Clover: "WARNING - Decide for yourself."
  • Crimzon Clover WORLD IGNITION changes it to "WARNING - Brace yourself!"
• Ketsui: "Approach your target and attack! Your mission starts now! Are you ready?"
• Space Invaders Infinity Gene:
  • For midbosses: "EMERGENCY — ELIMINATE THE UNEXPECTED ENEMY."
  • For major bosses: "WARNING — A FORMIDABLE ENEMY (name of boss) HAS ENTERED THE BATTLE."
• Rez, as part of its Extreme Graphical Representation of hacking: "The system is trying to shut down, trapping you inside! Defend yourself until (boss) is destroyed or self-destructs!"
• When you encounter Yokozuna Jr. in Contra: Shattered Soldier, a warning siren appears. It's actually one of the only ones in the entire series. Also, whenever you encounter a boss in Hard Corps: Uprising, "WARNING" appears onscreen, followed by the boss name. The only exception to this is the Final Boss, Tiberius.
• In Iron Tank, when approaching certain bosses, you receive the radio message "Watch out, use radar, gigantic enemy objects ahead!", and the music is overridden by an engine-like sound. An actual siren plays when a long-range turret boss activates.
• Blazeon starts looping the boss alert sound when enemies are still on the screen. After the last enemies scroll off, the following "Alarm Messages" appear in succession (the second over a Speed Stripes transition):
  Confirm the High Energy Core—Immeditely (sic) Change Main Reactor to Hyperdrive
  Release Hyper-drive and Return to Normal Drive Mode to Get Out of Warp—Set Up Destination in Real Time
  Change the Main Reactor Power to Attack Mode
• Raiden V has this in a first for the series. "Enemy flight battleships are approaching! Good luck!"
• Twinbee, possibly the Ur-Example, has a buzzer warning of an approaching boss. The NES sequel Stinger uses a klaxon and Epileptic Flashing Lights.
• Tyrian sometimes warns the player with "Large enemy approaching!". Not always, though.
• In Demonstar: "Time to take this bad boy down!"
• Super Earth Defense Force uses Dramatic Thunder to herald an end stage boss, even in locations where it wouldn't make sense (e.g. a cavern, the vacuum of space, or the alien base interior).
• Notebook Wars Ultimate displays a yellow "boss incoming" warning before a boss.
• Frantic: There's always "WARNING" in the center and "MASSIVE ENTITY DETECTED" flashing underneath/scrolling above and below it before a boss shows up.
• Psyvariar seems to take a page out of Darius, and the Updated Re-releases Psyvariar Revision and Psyvariar Delta also voice it:
  WARNING
  THE AREA TARGET
  (boss name)
  IS APPROACHING FAST
• Hydorah keeps things simple by simply having a machinal voice proclaim "PREPARE TO DIE!" as you are about to face down one of it's many bosses, and die you will.
• Aero Fighters 3 has the siren accompanied by the announcer: "Hey, you idiot! Make a move, or you will be finished! Show me what you've gooooooooootttttttttttttttt!!"
• Jets'n'Guns lacks a siren, but it does have a splash before boss battles.
  WARNING!
  BOSS CLASS ENEMY / FLYING MAUSOLEUM / DRUNKEN MASTER OF DELIRIUM AHEAD!
• ZeroRanger features a warning for minibosses and a longer, more dramatic warning for stage bosses. The stage boss warning is also accompanied by some Radiant Silvergun-esque tips on the boss's abilities.
• Whenever a boss is encountered in Sol Cresta, the following message says: "WARNING: A big enemy is approaching at full throttle. There is a huge hostile reaction. Intercept it with a perfect attitude. Ready to fire." It's yellow for mini-bosses while it's red for main bosses.

Simulation Game

• Project Wingman: Every time an elite squadron or an enemy ace pops out at the end of certain Campaign missions (or at the end of every Conquest map), a loud horn accompanied by the words "CAUTION - SQUADRON NAME" with a translucent insignia fills the screen when they spawn. Mostly associated with Crimson Squadron, the game inverts it during the last phase of the Final Boss Crimson 1. This time, the words "CAUTION - …" appears, with Monarch’s insignia in the background, meaning YOU have your own Boss Warning Siren.
• Ace Combat Zero: The Belkan War: Enemy ace squadrons get their own subtitles and introductory cutscenes when they show up. Your own squadron also gets this at the beginning of the game, and coincidentally, one of them is the Final Boss.
• Plantasia: Black clouds appear on the screen before a Zerg Rush of pests and/or weeds is about to attack the garden.

Survival Horror

• If you dig too deep in Dwarf Fortress, a warning will appear: "Horrifying screams come from the darkness below!"
• In the Silent Hill franchise, an air raid siren sounds just before the town shifts from fogbound to otherworld.

Third-Person Shooter

• In Splatoon 3's Salmon Run mode, a King Salmonid's arrival is heralded by a loud klaxon interrupting a distorted remix of the standard post-game victory jingle, as the word "EMERGENCY!" flashes onscreen.

Tower Defense

• While GemCraft: Chasing Shadows has Mooks, but no Bosses, the arrival of an Elite Mook (Apparitions, Specters, Shadows, and Spires) is heralded by an ominous black flickering at the edge of the screen; the stronger the flickering, the stronger the mook, and the sooner it will arrive. Later in the game, the flickering will occasionally herald an appearance by The Forgotten herself, though she only engages in Interface Screw rather than fighting you directly.
• Infinitode: The game displays a red "Boss wave" warning on top of the screen when the boss wave starts.
• Plants vs. Zombies: A warning appears for every flag wave, as well as a separate warning for the final wave of a level along with a "thud" sound effect.
  A HUGE WAVE OF ZOMBIES IS APPROACHING!

Non-Video Game Examples

• This is probably the Ur-Example: In the original version of Game of Death: In the second filmed fight, Hapkido master Ji Han Jae switches on a red light and warns Hai Tien and his associates to not progress any further or otherwise he will have to kill them.
  Ji Han Jae: As you gentlemen know, red means danger. Therefore I advice to you people, not to step into this warning arena. If you want to go on living, stop here, go back downstairs. Life is precious.
• Puella Magi Madoka Magica has curtains opening and a countdown from "5," flashing on the screen before Walpurgisnacht appears.
• Puella Magi Madoka Magica The Movie: Rebellion has this during the movie's climax, where a very similar countdown indicates Homulilly's attack. Coupled with Boss Subtitles in runes.
• Steven Universe gives a Shout-Out to Darius, as it seems that the ship Lars and the Off-Colors steal is equipped with an automatic warning system identical to the "Warning" display from Darius, and Rhodonite, acting as a Bridge Bunny, shouts "a huge battleship is approaching fast."
• Used regularly in Kill Bill when the bride has to fight a miniboss
• In NES Godzilla Creepypasta, the arrival of the villain/boss Red is preceded by ominous drumbeats and a single-word text warning: RUN.
• In Digimon Adventure: (2020), Monster of the Week Zanbamon's nightly appearances are preceded by two long blasts on a war horn.
• In Avataro Sentai Donbrothers, right before a defeated Hitotsu-Ki grows into their Hitotsu-King form, a siren can be heard.

---