Sherman Eisner didn’t start out as a businessman.

The accounting major and former Army platoon leader in Vietnam worked three decades at the Treasury Department, where one of the best things about his job was his office view of the Jefferson Memorial.

The day he interviewed at Treasury was one of the most memorable days of his life. Not because he got the job, but because he ran into a fellow Army officer who he thought had been killed in the jungle.

“Here was this guy,” he said, nearly choking up as he related the story to me. “One side of his face was heavily bandaged. He had been shot in the jaw with an AK-47 round. I was told he was dead. I couldn’t believe it. I remember sitting down with senior people at Treasury, and I stopped them. I said, ‘I hope I get this job, but my day has been made.’ And I told them the story of what had just happened.”

He got the job.

And he got perspective.

Eisner, 69, retired 14 years ago from his $110,000-per-year Treasury job at the relatively young age — to me, anyway — of 55.

As a 58-year-old, I am one of millions of baby boomers trying to figure out their next act and how to keep a paycheck coming in.

Eisner has figured that one out.

Since the mid-1990s — beginning while he was still at Treasury — the entrepreneur has been earning a nice side income from an alarm company. He is president of A&E Home Security Co., based above the garage at his Silver Spring home.

“I was able to very easily move from my government position into a business that was already a going concern,” he said. “There was no anxiety about, ‘What . . . am I going to do next?’ ”

He won’t tell me what he earns from his one-man alarm sales business, but it grosses $600,000 a year. That helps pay for his wife’s Prius, his 2002 Lexus (with 164,000 miles), his tennis fees, his woodworking hobby (he makes cedar kayaks and furniture), and his trips to places like London and Bryce Canyon National Park in Utah.

His advice to those approaching retirement is to look for something comfortable that you enjoy doing. “See how you can take that and move it into a part-time business venture.”

A&E sells two kinds of alarms. One triggers those annoying sirens that wail (for four minutes) across the neighborhood, waking everyone up. The other is known as a central station monitoring system, which sends a signal over a phone line or through a cellular device, notifying a 24-hour watchdog company that there may be a problem at the house. If the alarm goes off, the watchdog calls the house to see whether everything is in order. If they are not satisfied, they notify the police.

Eisner sells the kits and parts for the gear. We are talking about devices that attach to your windows and doors, motion detectors (they are actually infrared sensors) and the wall panels.

His standard order is $400, but amounts can be as little as $50 or as high as $2,000. About 25 percent of his business is commercial, while the rest is residential.

Most of his income is from sales, although he also collects a nice monthly dividend from telephone monitoring firms that administer the alarms.

Like any middleman, Eisner makes his money by buying from manufacturers, marking up the equipment, then selling it to customers. A big chunk of his orders are shipped by the manufacturer, which doesn’t require him to tie up his cash buying inventory.

“I get a lot of referrals, a lot of repeat customers, so I don’t have to walk them through it. Sometimes, cousins and families want on, and then a brother and sister wants an alarm. It does have a way of blowing out like that.

“It’s a comfortable business,” he said.

I’ll say.

Each morning, after walking his cockerpoo “Tobey,” Eisner heads to his office above the garage located at the end of a cul-de-sac. He works for a few hours, reviewing the overnight e-mails, Web orders and phone messages.

Eisner said he adds value by coaching customers on what to buy and whether they should attempt to install it on their own.

“I call people back and see what the issue is,” Eisner said. “The first thing I ask you is, ‘Are you mechanically inclined or do you have someone to install it?’ ”

Requests from customers range from part replacements to entire alarm system purchases to advice on how best to protect their home. If Eisner has a technical question that he can’t solve, he refers them to an Arlington firm called N&D Security, with which he has an informal agreement to back him up.

The idea for the business started in 1979, when his daughter was 11. Eisner and his wife, Ellen, decided to set up a home security system to take the place of babysitters. He didn’t have enough money to hire a company to install the system, so after some investigating, he happened upon a do-it-yourself kit from Ademco.

“They informed me that the only way I could purchase their equipment directly, and at their wholesale price, was to place an initial order over $2,500.”

Although he only needed about $350 worth of equipment, he teamed up with friends and neighbors, collecting $2,500 in orders. Word got around, and he started getting calls from strangers asking to purchase equipment.

The entrepreneurial light bulb went off, and a part-time business was born.

“I thought I could fill a need by selling people this equipment,” he said.

The first few years, he would take a week’s vacation from the Treasury and set up a booth at the Washington Home Show at the D.C. Convention Center, which produced most of his customers.

In 1996, he and his wife made a bold decision: They created a company Web site on the nascent Internet.

The Web site immediately started bringing in orders of $300 to $400.

“I was shipping all over the United States,” he said. “I was shocked.”

All the payments are done through credit cards and PayPal, the online payment system. Because he requires payment up front, he rarely gets stiffed.

A&E Security has afforded him a comfortable retirement, allowing him to do volunteer work in addition to his tennis and travel.

He has a healthy, buoyant attitude for a guy who spent a year avoiding booby traps and pacifying villages in the jungles of Vietnam.

Eisner, who grew up in New Jersey, was drafted after graduating from the University of Bridgeport in 1967 with an accounting degree. After officer’s candidate school, he was assigned to the Americal Division as a second lieutenant.

“Five of us entered the battalion together. Two of us went home together,” he said. “What happened to the other three, I don’t know. I just thought I would be very lucky if I got wounded and got back to the states.”

Maybe 55 wasn’t too young to retire. He earned it.