The X-Sense XS0B-MR121 smoke detector kit includes 12 wireless photoelectric smoke detectors (XS0B-MR) and 1 SBS50 base station (gateway). It features audible alerts with room identification (17 preset locations), full wireless connectivity (all detectors activate simultaneously), smartphone notifications via the X-Sense Home Security app (requires SBS50 and 2.4 GHz Wi-Fi), CR123A rechargeable batteries, and a mute function. The SBS50 base station supports expansion up to 50 devices (smoke detectors, CO detectors, water sensors, etc.). Detectors should be replaced after 10 years.