Arc Axe (5e Trap)
From D&D Wiki
This trap uses a pressure plate to trigger a swinging axe.
The DC is 15 to spot the pressure plate, as well as cut marks on the floor and walls.
The trap activates when more than 20 pounds of weight is placed on the pressure plate, causing the axe to swing at everything on the pressure plate. The axe makes a single attack roll with a +6 bonus. On a hit, it deals 1d12 slashing damage.
Wedging an iron spike or other object under the pressure plate prevents the trap from activating.
The axe has AC 15 and 18 hit points.