NEWARK -- The presence of a working smoke alarm saved an elderly couple from a fire that destroyed their home early Tuesday morning, an Alameda County fire official said.

The one-alarm fire in a three-bedroom, single-story home at 6065 Rockrose Drive near Mowry Avenue broke out just after 12:35 a.m., Battalion Chief Terrence Carey said. Crews arrived to find the home engulfed in flames and heavy smoke coming from the attic, Carey said.

The husband and wife were outside the home when fire crews arrived, Carey said. Both were awakened by the smoke detector, he said, and escaped the home before the flames spread.

"The smoke alarm saved their life. I can say that unequivocally," Carey said. "It alerted them to what was happening." Without it, there might have been a different outcome, he said.

Firefighters controlled the fire within 20 minutes and kept it from spreading to a nearby home, Carey said.

No injuries were reported as a result of the blaze, Carey said, but the residents were displaced and were going to live with relatives. Investigators have not determined what caused the fire.

Contact Rick Hurd at 915-945-4789 and follow him at Twitter.com/3rdERH