Poison Needle

From Dungeon Master's Guide, page 123.

Mechanical trap

A poisoned needle is hidden within a treasure chest's lock, or in something else that a creature might open. Opening the chest without the proper key causes the needle to spring out, delivering a dose of poison.

When the trap is triggered, the needle extends 3 inches straight out from the lock. A creature within range takes 1 piercing damage and 11 (2d10) poison damage, and must succeed on a DC 15 Constitution saving throw or be poisoned for 1 hour.

A successful DC 20 Intelligence (Investigation) check allows a character to deduce the trap's presence from alterations made to the lock to accommodate the needle.

A successful DC 15 Dexterity check using thieves' tools disarms the trap, removing the needle from the lock. Unsuccessfully attempting to pick the lock triggers the trap.