Audible Base GSA-AB4G - This base is designed for use where localized or group alarm signaling is required. When the detector senses an alarm condition, the audible base emits a local alarm signal. The optional GSA-CRR Polarity Reversal Relay can be used for sounding to other audible bases on the same 24 Vdc circuit. All detector mounting bases have wiring terminals that are accessible from the “room-side” after mounting the base to the electrical box. The bases mount to North American 1-gang boxes and to 3 1⁄2 inch or 4 inch octagon boxes, 1 1⁄2 inches (38 mm) deep. They also mount to European BESA and 1-gang boxes with 60.3 mm fixing centers. The GSA-SB4, GSA-RB4, and GSA-IB4 mount to North American 4 inch sq. electrical boxes in addition to the above boxes. They include the GSA-TS4 Trim Skirt which is used to cover the “mounting ears” on the base. The GSA-AB4G mounts to a 4” square box only.