Bethesda entrepreneur Greg Merril has invented a device which measures concussions on football helmets. The company is called Brain Sentry. (Kate Patterson/For The Washington Post)

Bethesda entrepreneur Greg Merril has built several companies around making technology user-friendly for common folks like me, who are allergic to instruction manuals.

One company went pfffffft! But another was a home run that landed him $12 million, a souped-up Porsche and a house in a leafy corner of Bethesda.

Now he is on to Brain Sentry, a 1-ounce, 3-inch-by-1-inch sensor that attaches to the back of a football helmet and lights up when the wearer gets whacked hard on the head. The light goes on. The coach sees it. Time to ask the player to count the number of fingers the coach is holding up.

With football training around the corner, Brain Sentry seems well timed, especially given concerns over concussions and head trauma.

“This ties to my skill . . . to create technology that must live with the people who use it,” said Merril, 49.

He isn’t the only local businessman in the concussion space. Christopher Tavlarides and Jimmy Lynn invested in a Seattle software company called X2 Biosystems, which makes software for tablets that helps diagnose concussions among athletes.

Merril owns 25 percent of Brain Sentry, which has raised more than $2 million from several investors, including Bethesda-based Hull Street Capital and Sam Medile, a parking company owner and former University of Maryland football player. Brain Sentry also has angel money from New York and Richmond.

The company has six employees who work in a 2,500-square-foot office in Bethesda.

Last month, the Arena Football League became the first professional sports league to require helmet-mounted sensors. The Brain Sentry Impact Counter, as Merril’s gizmo is called, was selected to assist coaches and trainers in identifying players who need to be examined for a possible concussion, according to the league’s Web site.

The company has more than 4,000 sensors in use around the United States, some for test programs and some for paying customers. It charges a subscription fee of $75 per player for the first year and $55 per year after that. The device is replaced each year.

Merril, who grew up in Rockville, has science in his blood. His father was chief of the biochemical genetics laboratory at the National Institutes of Health. His older brother is a physician who runs a Reston-based medical education company called Astute Technology.

Merril attended Western Maryland College, now known as McDaniel College, graduating in 1987 with a degree in psychobiology.

Millions of children across the country suffer from sports-related concussions every year. If they're not identified and treated quickly, the effects can be devastating and permanent. Bethesda-based Brain Sentry is trying to address that problem with a new, affordable piece of technology. (Gabe Silverman and Marina Cracchiolo/The Washington Post)

Two weeks after he graduated, the young entrepreneur, who had a knack for filmmaking, incorporated a company called High Techsplanations. The idea was to use video as a replacement for instruction manuals.

“I thought, ‘Why don’t I take my interest in arts and create a company that explains hi-tech things?’ ” He lived in his parents’ basement in Rockville while he cold-called companies such as DuPont and Bio-Rad Laboratories in California.

He landed a $5,000 video job from Bio-Rad, where a relative worked and his father’s reputation carried weight. But after a while, Merril realized there wasn’t any money in making one-off films for big companies.

“What I really wanted to do was create educational content that could be sold over and over again . . . to make the business scalable,” he said.

He and his brother, who was finishing medical school, talked about the difficulty would-be physicians experienced in learning how to perform minimally invasive surgeries like endoscopies, in which a tube with a camera is inserted down the throat to photograph the stomach.

He teamed up with Silicon Graphics, one of the hot technology companies of the ’90s, to put together a demonstration of a machine that simulated surgery using 3-D computer models. His team assembled and shipped the simulators from a 20,000-square-foot facility in Montgomery County.

High Techsplanations became HT Medical Systems, which built surgical simulators that cost between $10,000 and $30,000. Thousands have been sold.

The company grew to 70 employees, including a sales force in Europe and the United States. HT eventually became part of San Jose, Calif.-based Immersion Medical in 2000 in a $42 million transaction.

Merril walked away with $12 million.

“I got rich on that,” he said.

He bought a house in Montgomery County and indulged his interest in sports car racing. He bought a Porsche GT3.

He stayed with Immersion until 2002, but he quit auto racing after his first child was born in 2001.

His next big thing was to put some exercise into sedentary video games. He and an HT engineer created a four-foot joystick that allows a gamer to control their virtual character by using their whole body.

“We positioned the product as an exercise machine that was fun,” Merril said. “We ended up building these human-size joy sticks to measure how hard you push and pull.”

That company did well until funding dried up in the financial crisis of 2008.

After a couple of years working in management at local companies, Merril heard about firms that were helping with brain injury assessments of soldiers in Afghanistan and Iraq.

A light went off — again.

“I started to realize that everyone is talking about concussions,” Merril said. “I thought it would be great if we could improve diagnostics on the sidelines for football. Then I started looking at what has to happen with these injuries. It doesn’t matter how good you are at diagnosing a concussion. . . unless you know who to assess.”

Because many players — including kids — are reluctant to self-report after getting their bell rung, “we needed to figure out which kids got hit really hard in the head, and see which need to be taken aside and asked if they are okay,” Merril said.

Once again, he wanted to keep it simple, tailoring the technology to the parent who wants to safeguard their child, but doesn’t have time to manage a complicated device.

“If this is going to work, it has to be so easy it just works without me doing anything. I can’t have an on/off switch. No synching to a mobile device. It just has to work.”

It also had to be self-contained, waterproof, tiny and lightweight. No charger. Merril partnered with an engineer from HT Medical Systems, and they came up with a prototype.

He and the engineer founded the company together. Merril tapped into his network to find funding. He met Medile at Maryland’s Dingman Center for Entrepreneurship and got a $25,000 check on the spot. Former Redskins great Charles Mann, who uses the same attorney as Merril, joined the company’s board and invested. Merril bumped into Chris Meyers of Hull Street Capital at a neighborhood meeting and got another commitment for money.

Merril found a contractor in Raleigh, N.C., to manufacture the sensor. He got an Annapolis youth football team to test the device. In January of 2012, he introduced it at an American Football Coach’s Association Conference, where he met the commissioner of the Arena Football League.

This year, Brain Sentry hopes to have 20,000 sensors on helmets, generating up to $1 million in revenue. Nothing complicated about that.