This staff can be wielded as a magic quarterstaff that grants a +2 bonus to attack and damage rolls made with it.

Condition. To set a target for staff you need to know the targets face or  you need to have part of the target (blood, hair, nails....etc.) The staff will be set when target enters 15 foot radius. If the target is in the radius but not in the "line of sight" of the staff, it will not goes off.

Thunder killer. When the staff goes off it emits a crack of thunder, audible out to 300 feet. The target that was selected in preparation, must succeed on a DC 17 Constitution saving throw or become stunned until the end of your next turn. If the target is  in 15 feet radius he must make a DC 17 Dexterity saving throw, taking 9d6 lightning damage on a failed save, or half as much damage on a successful one. Target is the only one affected by the damage, but all creatures are affected by the sound and light.

Preparing and activating the trap. You can use an action to prepare the Thunder killer and additional action to conceal it with proper equipment. To staff is inactive until the user says the words “Death loud as thunder, death fast as lighting.”

Looks. This staff was design to be concealed in room and be prepared to strike. It look exactly like broom stick with no obvious differences.

Notes: Bonus: Magic, Damage: Lightning, Damage: Thunder, Deafened, Stunned, Damage, Control, Debuff, Combat