Test monthly by pushing the test button. If battery powered, change the battery at least once, preferably twice a year. An easy way to remember is, when you change your clock in April and October - change your battery. These are not required by law, but are desirable. When the detector activates, evacuate the house, open windows and doors, and contact the gas company or plumber to check gas appliances.
Detectors are likely to go off in the winter months when houses are closed up and heaters are on.
If your detector sounds an alarm and if anyone in the house has a headache, feels nauseous, or ill, call the fire department.