Chris Hanrahan walks five miles a day just running around his game store in downtown Oakland. He knows exactly how many steps he takes thanks to a tiny tracker in his pocket called a Fitbit.
"It's changed my life basically," Hanrahan said.
It is one of a growing number of wearable electronics that has people wiring up to lose weight.
Hanrahan says he "went from like a XXL to a medium and a 40-inch waste to a 29-inch waist." He started using the Fitbit about two years ago.
"I hate exercising with a passion, and walking to me isn't exercise," Hanrahan said.
Stores like the Best Buy on Harrison Street in San Francisco have struggled to keep them in stock.
"At one point there was such a large demand, you know, they were just flying off the shelves," Best Buy fitness expert Mohammed Bukhari said
Two San Francisco companies are leading the pack.
Jawbone and Fitbit track your movement during the day and record your sleep pattern at night. They also come with free apps that help you keep track of the number of calories you burn and eat. Enter in what you ate on the Fitbit app, or just scan a barcode with the Jawbone app.
Fitbit released its newest device last month, the Flex Force.
"We've grown from 80 employees to 200 employees the past two years; our products are carried in over 20,000 stores worldwide," Fitbit co-founder James Park said.
He got the idea from the Nintendo Wii, the first game that allowed people to interact with games by moving.
"I was just really amazed at the way Nintendo combined sensors, motion sensors with software, and really changed the way people thought about gaming," Park said.
That technology has evolved into a number of wearable devices and scales to help people get trim.
Travis Bogard heads up Jawbone's wearable fitness category. "We know there's this huge gap between intention and action - what people think they are doing and what they are actually doing," he said.
Jawbone's wearable fitness device is called UP.
"The band tracks your movement throughout the day passively, and your sleep at night, and then in the application you can see what you are doing," Bogard said.
Both the Jawbone and Fitbit apps allow you to set goals and share them with your friends on social media. The Fitbit Flex and jawbone UP both cost just under $130.
Sharon Meyer is a nutrition counselor at California Pacific Medical Center in San Francisco. She's recommended wearable fitness trackers to patients.
"It's trackable," Meyer said. "Whereas before, it's 'Well, I think I did this, maybe I'll do that,' but if you've got something that is trackable and traceable, I think that is one of the reasons people can people can do so much better with those things. "
Chris Hanarah says he can't stop telling people about how tracking his steps improved his health.
He said it's been a, "fantastic experience, I've recommended it to a ton of friends who are also seeing results."
Written and produced by Ken Miguel