... Interconnectable feature(carbon monoxide detector,CO sensor, CO detector) 1. Non-radioactive technology for environmental friendly2. CO concentration threshold: varying time- ... battery tamper resist feature5. Inter-connectable up to 40 CO, Heat And/Or Smoke Alarms6. 2 color LED ... missing warning indicator8. Hush/Test button9. Auto-reset when CO clears10.CE, TUV approved, comply with EN50291, UL ...