ZSlayer Boss Proximity

Immersive horror audio when bosses are nearby — heartbeat, heavy breathing, and dread

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Your heartbeat pounds. Your breathing gets heavier. Something is close. A client-side BepInEx plugin for SPT that plays escalating heartbeat and heavy breathing audio when you're near a boss in raid. Closer = louder, faster, bassier. Horror game feel.

Discord | YouTube | Releases

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What Is This?

A lightweight client-side mod that adds proximity-based horror audio to raids. When you're within range of any boss (Tagilla, Reshala, Killa, Sanitar, etc.), your character's heartbeat starts pounding — getting faster, louder, and bassier the closer you get. Get within 20m and heavy breathing layers in. Kill the boss and the audio smoothly fades away.

Works with all 21 vanilla boss types plus custom modded bosses via config. No server mod required — pure client-side immersion.

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Features

Heartbeat System Escalating heartbeat audio driven by boss distance. 40m range — heartbeat starts at the edge of detection BPM scaling — 60 BPM at max range, 140 BPM at point-blank Volume scaling — faint at distance, pounding up close Low-pass filter — audio gets bassier and more muffled as you close in (2000 Hz → 600 Hz) Timer-based playback — each beat is a discrete thump, not a looping track	Heavy Breathing Layered breathing audio for extreme close range. 20m range — breathing kicks in when you're dangerously close Volume scaling — silent at 20m, intense at point-blank Pitch scaling — breathing gets faster as proximity increases (0.9x → 1.1x) Seamless loop — continuous breathing audio with crossfade
Smart Detection Efficient boss tracking with minimal performance impact. 21 vanilla boss types tracked (Reshala, Killa, Tagilla, Sanitar, Gluhar, Knight, Big Pipe, Bird Eye, Kolontay, Partisan, Zryachiy, and more) Custom boss IDs — add modded bosses via config Event-driven — subscribes to spawn/death events instead of polling Nearest-only — only the closest boss drives audio (no stacking) 10 Hz update rate — distance checked every 0.1s for smooth response	Smooth Transitions No jarring audio cuts — everything fades naturally. Fade-in — audio ramps up smoothly when entering range Fade-out — audio ramps down when leaving range or boss dies Lerp-based — all values (volume, BPM, pitch, filter) smoothed per frame Configurable speed — adjust fade responsiveness via config
Audio System Ship real audio files or let the mod generate its own. WAV file support — drop heartbeat.wav and breathing_loop.wav in the Audio folder Auto-trim — long recordings are trimmed to a single beat on load (0.5s) with fade-out to prevent clicks Procedural fallback — if no WAV files are present, generates heartbeat (layered sine waves with lub-dub envelope) and breathing (filtered noise with inhale/exhale cycle) at runtime 2D audio — non-directional (it's YOUR heartbeat, not the boss's)	Fully Configurable All settings exposed via BepInEx config (F12 in-game). Setting Default Description Enabled true Master toggle HeartbeatRange 40m Detection distance MinBPM / MaxBPM 60 / 140 BPM range MinVolume / MaxVolume 0.15 / 1.0 Volume range BreathingRange 20m Breathing distance BreathingMaxVolume 0.8 Breathing volume FadeSpeed 3.0 Transition speed CustomBossIds (empty) Modded boss IDs

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Quick Start

Download the latest release from Releases and extract into your BepInEx plugins directory:

EscapeFromTarkov/
└── BepInEx/
    └── plugins/
        └── ZSlayerBossProximity/
            ├── ZSlayerBossProximity.dll
            └── Audio/
                ├── heartbeat.wav        ← optional (procedural fallback)
                └── breathing_loop.wav   ← optional (procedural fallback)

Launch the game and load into any raid with a boss. That's it — no configuration needed.

To customize settings, press F12 in-game to open the BepInEx config manager.

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How It Works

┌─────────────────────────────────────────────────────────┐
│                    IN RAID (Update Loop)                 │
│                                                         │
│  BossTracker (10 Hz)                                    │
│    ├── Maintains alive boss list via GameWorld events    │
│    ├── OnPersonAdd → check IsTrackedBoss → add          │
│    ├── UnregisterPlayer → remove                        │
│    └── Calculates nearest boss distance                 │
│                                                         │
│  ProximityAudioController (every frame)                 │
│    ├── Reads ClosestBossDistance from tracker            │
│    ├── Heartbeat (40m → 0m)                             │
│    │   ├── BPM: Lerp(60, 140, proximity)                │
│    │   ├── Volume: Lerp(0.15, 1.0, proximity)           │
│    │   ├── LowPass: Lerp(2000, 600, proximity) Hz       │
│    │   └── PlayOneShot on timer interval                 │
│    ├── Breathing (20m → 0m)                             │
│    │   ├── Volume: Lerp(0, 0.8, proximity)              │
│    │   └── Pitch: Lerp(0.9, 1.1, proximity)             │
│    └── All values smoothed via Mathf.Lerp per frame     │
│                                                         │
│  Harmony Patches                                        │
│    ├── GameWorld.OnGameStarted → create tracker + audio  │
│    ├── GameWorld.OnDestroy → cleanup                     │
│    └── GameWorld.UnregisterPlayer → remove dead boss     │
└─────────────────────────────────────────────────────────┘

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Tracked Bosses

All 21 vanilla boss roles are tracked by default:

Boss	Role ID	Map
Reshala	bossBully	Customs
Killa	bossKilla	Interchange, Streets
Tagilla	bossTagilla	Factory, Streets
Sanitar	bossSanitar	Shoreline
Gluhar	bossGluhar	Reserve
Shturman	bossKojaniy	Woods
Knight	bossKnight	Various
Big Pipe	followerBigPipe	Various
Bird Eye	followerBirdEye	Various
Kolontay	bossKolontay	Streets
Partisan	bossPartisan	Various
Zryachiy	bossZryachiy	Lighthouse
Boar (Kaban)	bossBoar	Streets
Cultist Priest	sectantPriest	Various (night)
Santa	gifter	Seasonal
Arena Fighter	arenaFighterEvent	Various
Legion	(WildSpawnType)199	Various
Punisher	(WildSpawnType)801	Various

Modded bosses: Add integer WildSpawnType IDs in the CustomBossIds config entry (comma-separated).

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Roadmap

Future features planned for integration into this mod:

Status	Feature	Description
Done	Boss Heartbeat	Escalating heartbeat + breathing near bosses
Planned	Cultist Whispers	Eerie whispers and murmurs when near Cultists — layered audio that intensifies with proximity, especially unsettling during night raids
Planned	PMC Proximity Dread	Low, unsettling drone audio when an enemy PMC is within ~50m — no directional information, just the creeping awareness that someone is close. Teammates excluded.

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Tech Stack

Component	Technology
Plugin	C# / .NET Framework 4.7.1, BepInEx 5.x
Patching	Harmony via SPT ModulePatch
Audio	Unity AudioSource + AudioLowPassFilter, custom WAV loader, procedural generation fallback
Detection	GameWorld events + WildSpawnType role matching

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Requirements

	Version
SPT	4.0.x
BepInEx	5.x (bundled with SPT)
FIKA	Not required

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FAQ

Does this work without FIKA?

Yes. This is a pure client-side mod with no server dependency. It works on vanilla SPT and with FIKA.

Does the server or other players need this installed?

No. Only install it on your own game client. It has no server component and no multiplayer impact.

Can I use my own heartbeat audio?

Yes. Drop any 16-bit PCM WAV file named heartbeat.wav in the Audio/ folder. Long recordings are automatically trimmed to a single beat (0.5s). Same for breathing_loop.wav (not trimmed — should be a seamless 3-4 second loop).

Will it affect performance?

No measurable impact. Distance checks run at 10 Hz (not every frame), boss tracking is event-driven, and audio uses Unity's built-in AudioSource system.

What if no audio files are present?

The mod generates procedural audio at runtime — a synthetic heartbeat (layered sine waves) and breathing loop (filtered noise). It works out of the box, but real samples sound better.

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Contributing

This is a solo project by ZSlayerHQ, but feedback and bug reports are always welcome.

• Bug Reports — open an issue with steps to reproduce
• Feature Requests — open an issue or discuss on Discord

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MIT License — Built by ZSlayerHQ / Ben Cole