As players scavenge or complete quests, a "Noise/Threat" meter builds up. When full, it triggers a zombie siege on the player's camp.
It prevents the camp from feeling like a static, safe "menu" and makes it a living part of the world. Survival Nation Free Download (v1.01)
According to the official Survival Nation: Mobile and VR listings, the game already includes: As players scavenge or complete quests, a "Noise/Threat"