The BRK model no. 3120B is a wire-in, 120 V AC 60 Hz single and/or multiple station photoelectric and ionization dual sensor smoke alarm specifically designed for residential and institutional applications including sleeping rooms of hospitals, hotels, motels, dormitories and other multi-family dwellings as defined in standard nape 101. Model 3120B complies with UL217, CSFM, nape 72, HUD, fa and other agencies that model their codes after the.. See full description for further details