If your CO alarm chirps every 30 seconds, it's not an emergency but you should replace the CO alarm a.s.a.p. - Fire Line
First Alert Battery-Operated Carbon Monoxide Detector — Saber Sales & Service
How to Replace 9V Batteries in Smoke or CO Alarms
Which is Better: Hardwired or Battery Smoke Alarms? - National Safety Inspections
Replacing Back-up Batteries in Ei Electronics Alarms | An alarm without a battery will not alert you in the event of a fire. Test your alarms weekly & replace batteries when low #
How to test the batteries in smoke detectors at Batteries Plus