... Main Features: 1.Non-radioactive technology for environmental friendly2.CO concentration threshold: varying time-to-alarm depending on concentration3.With ... and battery tamper resist feature5.Inter-connectable up to 40 CO, Heat And/Or Smoke Alarms6.2 color LED indicator ( ... battery missing warning indicator8.Hush/Test button9.Auto-reset when CO clears10.CE, TUV approved, comply with EN50291, UL 2034 ...