{"id":94,"date":"2026-04-09T22:30:23","date_gmt":"2026-04-09T20:30:23","guid":{"rendered":"https:\/\/www.noocturnalgamesstudio.com\/blog\/2026\/04\/09\/stealth-mechanics-in-unity-building-npcs-that-hear-and-alert-each-other-without-spaghetti-code\/"},"modified":"2026-04-09T22:30:23","modified_gmt":"2026-04-09T20:30:23","slug":"stealth-mechanics-in-unity-building-npcs-that-hear-and-alert-each-other-without-spaghetti-code","status":"publish","type":"post","link":"https:\/\/www.noocturnalgamesstudio.com\/blog\/2026\/04\/09\/stealth-mechanics-in-unity-building-npcs-that-hear-and-alert-each-other-without-spaghetti-code\/","title":{"rendered":"Stealth Mechanics in Unity: Building NPCs that Hear and Alert Each Other Without Spaghetti Code"},"content":{"rendered":"
\n

Implementing a believable stealth system is one of the biggest challenges for any indie developer. It is not just about the enemy seeing you; it is about how the environment reacts when you make a mistake. The real problem arises when we try to make NPCs communicate. If Guard A detects the player and has to manually call Guard B, C, and D, you end up with spaghetti code full of direct references that break your project when a single object is removed from the scene.<\/p>\n

The Monolithic AI Trap<\/h3>\n

Traditionally, AI logic is written in massive scripts that try to handle everything: patrolling, vision, hearing, and combat. This is not scalable. At Noocturnal Games Studio, we believe the professional solution is total decoupling through an event-driven architecture.<\/p>\n

The key is not for NPCs to know each other, but for them to emit signals to the environment that others can listen to autonomously.<\/div>\n

Hearing Mechanics: SoundEmitter and SoundReceiver<\/h3>\n

For an enemy to hear your footsteps or a distraction, we need a propagation system. Instead of the player searching for all nearby enemies, the player emits a sound and interested parties react.<\/p>\n

Implementation with Modular AI Behaviour Kit:<\/h4>\n

\/\/ The player emits a sound upon landing
\nSoundEmitter.EmitSound(radius: 15f);<\/p>\n

\/\/ The NPC has a SoundReceiver listening for the event
\npublic void OnSoundHeard(Vector3 position) {
\n aiController.ChangeState(AIState.Searching);
\n searchBehavior.StartSearch(position);
\n}<\/code><\/p>\n

This approach allows any object (a rock, a grenade, the player itself) to generate sounds without knowing the AI exists. This is pure modularity.<\/p>\n

Social Coordination: The Alert System<\/h3>\n

What happens when a guard spots the player? In a professional game, that guard must shout. But we do not want to call specific functions of other guards. We use the Alerter component.<\/p>\n