When baby Alex cries, lights flash in every room in Joe and Meg Duarte's Centreville home. It's not that they're overly worried parents. Lights also blink when someone knocks at their front door or calls them on the telephone.

Such solutions have helped normalize life for the Duartes, who are among an estimated 28 million Americans with hearing loss. The couple's three children have normal hearing.

Four years ago, Joe Duarte decided to give up his engineer's job with International Business Machines Corp. to expand on what had been, until then, his basement hobby: using technology to help the deaf and hard of hearing. Meg, who had taught deaf children for several years, joined him.

The result was Duartek Inc., a small Fairfax company that Joe Duarte, 39, says "tries to make a difference" in the lives of people with hearing loss by educating them about the latest technology.

The Duartes and their six-member staff, most of whom have progressive or severe hearing loss, say some customers have been moved to tears when shown "that this is not a dead end in life," as he puts it.

When Mardie Younglof came to Duartek, "I thought I was deaf, and that was it. But Joe made me try on every listening device," she said. But she found out that a device with a microphone and an FM transmitter made the sound coming through her hearing aid clearer, making it easier to speech read. Younglof, born profoundly deaf after her mother contracted German measles during pregnancy, works for the company.

Joe Duarte was born with severe hearing loss but was diagnosed by physicians as mentally retarded until his mother, working with a primitive piece of equipment called an auditory trainer, proved them wrong.

That training device and the cumbersome microphone his college professors used are on display in the showroom alongside the latest products, including infrared and other sophisticated listening systems, vibrating alarm clocks, phones that clarify certain language sounds, defense aids that call out for help if the user cannot do so and a compact TTY (telephone typewriter) that is no bigger than a fat pocketbook.

In a small work space behind the showroom, Joe Duarte customizes some equipment, such as special lecterns he is building for Fairfax libraries and a "sound barrier chair" that shakes in tandem with the pounding action in movies such as "Jurassic Park." (A young boy who sat in it recently begged, "Mom, I must have this chair.")

In addition to one-on-one consultations, Joe Duarte has worked with the U.S. Department of Education, the Baltimore Aquarium and area churches, nursing homes, theaters and courthouses.

"The technology was available," Joe Duarte said, "but people didn't know what was best or how to use it."

Duartek's small staff treats its customers, and one another, like family.

Sara Franco, an employee who assesses clients' needs, said people who have progressive hearing loss often need emotional support. Many mourn the loss of their independence.

"They go through a kind of grieving," she said, speaking from personal experience.

"The reason we are all so involved is that there is a not-so-positive side to growing up hearing-impaired," she said, describing the hurt inflicted by others, often unwittingly, with a casual comment or funny glance.

"All of us are resolved to see that not happen to those coming up today."

Two years ago while traveling, Franco asked a hotel employee for a closed-caption decoder for the TV in her room. Under the Americans with Disabilities Act, hotels are required to have at least a few on hand. The clueless clerk disappeared for a few minutes, then returned clutching an ironing board.

"Fine," Franco said. "Where's the volume control?" CAPTION: Joe Duarte shows off listening devices and other tools at Duartek, his Fairfax-based company. He likes to explain how techonology can help people with hearing loss.