The Nassau County Police Department says the detective was passing by when he noticed flames coming from a home on Mineola Boulevard in Williston Park around 7:30 a.m. Sunday.
The detective and a resident of a neighboring home escorted the 59-year-old homeowner to safety. He's been taken to a hospital with smoke inhalation.
Some 100 firefighters from Williston Park, Mineola, Albertson and Garden City worked to douse the blaze. Two firefighters were treated at the scene for chest pains and heat exhaustion. A third firefighter was taken to a hospital with a sprained ankle.
The cause of the fire isn't yet determined, but police say it isn't considered suspicious.