Did you know that carbon monoxide detectors have an expiration date? Most are good for 5-7 years on average. Over the weekend, my hardwired smoke/ CO detector went off and would not reset. We decided to call the fire depatment just to be safe and they confirmed that the alarm was failing and needs replacement. On most CO alarms, there is a tag on the back or inside the battery compartment which will have a date of manufacture or an expiration date (as shown w/ pencil in photo). Always keep the instructions in an accessable place for quick reference if an alert should sound, or to confirm when yours needs replacement. Carbon Monoxide is a real hazard and if you have a gas burning appliance in your home you definitely should have at least one CO detector.