An apparatus, according to various aspects of the present invention, produces contractions in skeletal muscles of a target to impede locomotion by the target. The apparatus is used with a provided deployment unit that deploys an electrode away from the apparatus. The electrode conducts a current through the target. The apparatus includes a terminal; a producing sub-system for producing an electric arc to warn the target without conducting a current through the target; a conducting sub-system for conducting the current in series through the terminal and through the target; an initiating sub-system for initiating deployment of the electrode; and an operator interface. The operator interface facilitates selecting one or more cartridges of a set of cartridges to provide a stimulus signal to a target and/or display an arc.