Size: 5-Pack Combination Photoelectric Smoke Alarm and Carbon Monoxide Detector : Combines both photoelectric smoke and carbon monoxide detection in one device. Smoke Carbon Monoxide Alarm Detector : This alarm detector can provide early warning for potential dangers when smoke concentration reaches a preset threshold. Normal Operation Confirmation : A flashing green LED light every 60 seconds indicates the unit is actively monitoring for threats. Battery-Operated : Powered by 3 AA batteries(1 year lifespan) rather than being connected to an electrical source. making it easy to install and maintain. Before purchasing : Please check the product dimension(4.01 diameter, 1.37 thick)