Acid Sprayer (5e Trap)
From D&D Wiki
Acid sprayers are pressure plates with a hidden nozzle that spray acid at the victim when stepped on. Acid sprayers are deployed in rooms with large arrays of them, and just to add to the confusion a good number of them are inactive just to throw off unsuspecting victims. A creature can notice that a tile could be an acid sprayer with a successful DC(12) Perception check, and a further DC(15) Perception check to tell whether or not it is active.
An active acid sprayer automatically triggers when at least 10 pounds of weight is placed on top of it, spraying acid in a circle that is 15ft in diameter. Any creatures caught in this circle take 4d10 Acid damage. A creature can attempt a DC(15) Dexterity check to avoid triggering the trap while walking over it. An acid sprayer can be disarmed by wedging objects under the pressure plate.
Inactive acid sprayers make a hissing noise when triggered, as if they are attempting to spray fluid but have no fluid to spray.