Xanathar's Guide to Everything
Simple Trap, Dangerous (1st–4th Level)
The crossbow trap is a favorite of kobolds and other creatures that rely on traps to defend their lairs. It consists of a trip wire strung across a hallway and connected to a pair of hidden heavy crossbows. The crossbows are aimed to fire down the hallway at anyone who disturbs the trip wire.
Trigger. A creature that walks through the trip wire triggers the trap.
Effect. The trap makes two attacks against the triggering creature. Ranged Weapon Attack: +8 to hit, two attacks; Hit: 5 (1d10) piercing damage on a hit. This attack can't gain advantage or disadvantage.
Countermeasures. A successful DC 15 Wisdom (Perception) Test reveals the trip wire. A successful DC 15 Dexterity Test using Thieves' Tools disables the trip wire, and a Test with a total of 5 or lower triggers the trap.