Technicians from Art Douglas Plumbing visited the homes of 25 seniors to install the detectors and perform safety checks on their heating systems.
The company says since many seniors live on fixed incomes they may not be able to afford maintenance on their heating units.
One technician who checked a Southeast Fresno home found elevated levels of carbon monoxide in the basement and a furnace that wasn't ready for winter.
"It's a safety measure that everybody needs to address because you never know," Steve Stock of Art Douglas Plumbing said. "This lady's lived with it for several years and never known she's been inhaling carbon monoxide. So it's more safety, safety, safety."
The Fresno-Madera Area Agency on Aging says it will keep track of any safety concerns discovered by the technicians.