A lever to open a door is in a small recess of a wall. If a player reaches into the recess to pull the lever, clamps quickly close to ensnare them at the wrist.
A rogue can disable the trap DC 15 (DC 25 if attempting to disable with one hand caught in the trap). Otherwise, brute force DC 15 for 1d6 collateral damage.
Player takes 1d10 damage each failed attempt to get free.
If not freed within 3 minutes, a pendulum swings down at the player, dealing 1d20 damage. On 20, the player loses the hand.
Hand illustration Creative Commons cc0.