A guide (1) for a firearm (500) is mechanically and electrically engageable by an accessory device (900). The guide (1) includes a coupling body (2) with two rows of teeth (21, 22) and, between them, an interaction surface (25), identifying interaction modules (250) including a pair of main holes (251) and a secondary hole (252). The guide (1) includes an electronic group (3) having an electronic board (31) and electrical contacts (30) divided into main pairs of electrical contacts (301) housed in the main pairs of holes (251) and secondary pairs of electrical contacts (302) each housed in a respective secondary hole (252). The guide (1) includes a switch group (4), operationally connected to electrical contacts (301, 302) suitable for moving the contacts between an inactive position and an active position upon the action of the accessory group (900) which is thus electrically connected.