You should check your HVAC system twice a year. Here are other things that should be monitored: Check smoke alarms and carbon monoxide detectors. It is recommended that smoke alarm batteries be replaced twice a year, and if your smoke alarm is between five and 10 years old, it should be replaced. Make sure there is at least one alarm on each level of your house, and one near each bedroom. The same placement recommendations go for carbon monoxide detectors, as well. Try to keep both detectors away from gas appliances and fireplaces, as each give off small amounts of carbon monoxide when first turned on and could trigger a false alarm.