DangerSense

DangerSense adds a single item, the Eye of Hostility. In its default mode it will warn of nearby hostile mobs by visually opening and colouring the edges of the screen. By holding the use key while looking at a mob, the Eye can be focused on that type of mob, only responding to it. To reset to Hostiles mode, hold the use key while not looking at a mob.
The range and definition of hostile can be configured via the configuration file & configuration tags.

Crafting
The Eye of Hostility is crafted shapelessly from 2 Redstone Dust, 2 of certain mob drops, and 1 Spider Eye.
By default the following mob drops can be used: Bones, Bone Meal, Gunpowder, Rotten Flesh, Spider Eyes.
The usable mob drops are configurable via tags.

Decay
The organic components of the Eye decay over time, it will turn into a Degraded Eye of Hostility after a default period of 4 days. The decay period is configurable, with a maximum of 2147483647 ticks (~3.5 realtime years).

Degraded Eyes do not function, but remember their focus. Crafting a Degraded Eye with a Spider Eye and 2 valid mob drops will repair it, keeping the focus. Alternatively it can be placed alone in a crafting grid to recover 2 Redstone Dust.

Ingame Screenshot
The overlay colour can be configured via the configuration file