Dangersense Potion

Anything in the world that can hurt or hinder you gets outlined in red, through solid rock and in complete darkness. That covers the obvious pressure plates and dart traps, but also the quieter hazards: thin ice over a drop, antlion eggs, a hive tucked into the jungle, a geyser, a boulder parked above a corridor, hellstone underfoot. Cobweb and honey blocks count too, since both stop you moving. The buff runs a long time and can be cancelled early by right clicking its icon when the red starts getting in the way.

This is what the potion is really for. Both places seed their floors with plates wired to things you cannot see coming, and reading them in advance turns a nervous crawl into a walk. It also picks out cracked bricks in the dungeon, so hidden rooms stop being hidden. If you want the mechanism rather than an intact ankle, the Mechanical Lens or The Grand Design exposes the wiring, and between the two you can take a trap apart instead of tiptoeing around it.

• Cobweb glows, so spider nests are visible from a distance and a trail of webbing usually points toward open cavern.
• If you are harvesting traps for your own arena or farm, this is the fastest way to find them in bulk.
• Drink one before fighting in an arena built with boulders or dart traps. You can watch the boss instead of the floor.
• Echo Coating hides nothing from it, because a coated object still throws off red particles.

A Dead Man's Chest is not flagged, though the trap wired into it is. A chest with red outlines all around it and nothing on the chest itself is the tell that the loot is the bait. As for supply, you rarely need to brew these: pots, chests and crates turn them up often enough that a working stack accumulates on its own.