Kidde HD135F Fyrnetics Hardwire Heat Detector with Battery Backup This product is highly durable Easy to use This product is manufactured in United States Interconnects with up to 24 Kidde devices including smoke and CO alarms 9-Volt battery back up Quick connect power harness makes installation fast and easy Test button tests unit's electronic circuitry Kiddes heat detectors meet the requirements of Underwriters Laboratories (UL), an independent facility that tests products for compliance with widely-accepted safety standards