Heating Help

Carbon Monoxide detectors

Hey - I have a few questions. My mother bought a house last year and her carbon monoxide detectors went off because of an issue with her wood stove. I heard that once the detectors go off, they need to be replaced. Is that true?? Ever since that time the detectors go off for some unknown reason. The went off last night with windows open. She has been using central air by day, but not at night. They had gone off several times and always at night. My mother is older and freaks out and can't shut them off on her own. I need simple detectors where there is an easy shut off switch. Can anyone help?? Thanks, Keven