Our CO detector was actually doing 5 quick chirps. According to the manufacturer website that means ‘time to replace’ because it is 5-7 years old. We have another one downstairs on the wall outside the hallway where the furnace closet is. That’s our only gas appliance inside (hot water heater is also gas but it’s outside so not an issue) so I’m not too worried but I still will order a new CO detector for upstairs.