The Universal Security Instruments MDS300-401 4-in-1 Universal Smoke Sensing Alarm provides quadruple the protection with only two installations. This set comes with (1) MDS300 IoPhic Smoke and Fire Alarm and (1) MCND401 Plug-In Carbon Monoxide and Natural Gas Smart Alarm to protect your family against four deadly household threats: fast-flaming fires, slow-smoldering fires, carbon monoxide and natural gas (or methane). Perfect for new or replacement installations, both alarms are suitable for houses, apartments and mobile homes. Universal Smoke Sensing Technology (IoPhic) responds 87-percent faster to slow smoldering fires and responds quickest to fast-flaming fires. This alarm has additional features including a self-diagnostics check, a sensitivity adjustment for changes in temperature or humidity and an end-of-service life warning that sounds when it's time to replace the battery. The MCND401 features a compact plug-in design that covers only (1) outlet for a fast and easy installation with no wiring required. This alarm has a digital display screen that provides carbon monoxide PPM (parts per million) levels and displays "GAS" during an occurrence. Peak CO levels are recorded with the memory button and (3) LED colors display the status of the alarm, power, CO and gas. Both alarms come with a 9-Volt alkaline battery that operates the alarm and continues protection in the event of a power outage. The Universal Security Instruments MDS300-401 4-in-1 Universal Smoke Sensing Alarm comes with a 10-year limited warranty on the MDS300 and a 5-year limited warranty on the MCND401. Founded in 1969, Universal Security Instruments has over 40-years of heritage in providing home safety products for families. Visit www.amazon.com/universalsecurityinstruments for more information on Universal Security Instruments and our extensive line of products.