Editor's note: This article is part of Inc.'s 2020 Best Industries report.

In February 2017, Donovan got lost during a trip to the park. The skittish rescue dog's owner Collette Bunton spent hours frantically searching before the rat terrier mix finally found his own way home. To make sure her beloved pet would never get lost again, Bunton did some research on tracking devices, and decided to fit Donovan's collar with a device from a San Francisco-based startup called Whistle.

Fifteen months later, Bunton received a surprise phone call from Whistle: Want to be our CEO? "You probably don't know us very well," said co-founder Ben Jacobs, the voice on the other end. Bunton, a former Roku and Logitech executive, could only laugh: "I know you, and I have ideas on what kind of things we could do."

With Bunton at the helm, Whistle has become a leader in the fast-growing pet wearables industry by rapidly improving its technology for monitoring customers' furry friends. Its flagship product line of Whistle Go devices--think of them as doggy Fitbits with cellular data-enabled location tracking--used to simply report a pet's location and number of miles walked per day. Now, that data gets crunched in real time to notify you through a smartphone app when subtle changes, like decreased activity or increased scratching, could indicate a health problem.

"You can, today, do things that you couldn't do six months ago," Bunton says. "There really is a true technology and use case inflection point that's happening."

Whistle's devices cost between $100 and $130, plus a subscription fee. Whistle declined to disclose specific revenue figures, but says it has seen consistent double-digit revenue growth rates since its launch eight years ago. Business intelligence platforms Owler and ZoomInfo estimate Whistle's annual revenue at $30 million and $38.9 million, respectively.

Developments like longer-lasting batteries and 5G technology have sped advances in pet wearables, according to Ross Rubin, founder and principle analyst at consulting firm Reticle Research. The next step, he says, will be to more heavily saturate the market with affordable products: "It's just a question of finding the right combination of cost and functionality."

The pet wearables market--which includes GPS and fitness trackers, cameras, and smart clothing--is expected to grow to $1.7 billion in 2024 from $703 million in 2019, according to data from research firm MarketsandMarkets, and Whistle estimates that more than a million devices have been sold industry-wide to date.

Striving for customization

Whistle was founded in 2012 by Jacobs, fellow ex-Bain consultant Steven Eidelman, and software engineer Kevin Lloyd. Growing up, Jacobs had a German shepherd named Bear who seemed perfectly healthy, but just days later had to be put down due to intestinal twisting. The founders' idea centered not around pet tracking, but on monitoring canine activity for predictive health, which could have caught Bear's issue sooner.

The startup attracted talent from companies like Apple and Google and grew thanks to more than $20 million in venture capital funding--until 2016, when it was acquired by Mars Petcare for $117 million. Jacobs credits Mars, Inc.--one of the largest privately owned companies in the U.S.--for allowing Whistle to continue operating independently under its new corporate umbrella.

Between 2017 and 2019, the three co-founders left the company. Eidelman and Lloyd departed for other startups, and Jacobs became head of ventures and partnerships for Kinship, Mars's pet-focused startup accelerator and $100 million venture fund. Enter Bunton, who had run Roku's devices department as a senior vice president and general manager from 2012 to 2014. Upon joining Whistle in June 2018, Bunton immediately set about shifting the company's ethos to prepare for the industry's anticipated growth.

Strategically, that involved amping up services like data collection and analysis, in addition to the company's focus on hardware. For example: Whistle's Pet Insight Project, in which dog owners receive the company's newest product, a Whistle Fit, for free in return for access to that device's activity, calorie burn, and mileage data. Whistle has collected data from more than 60,000 dogs across 900-plus different breeds and mixes, which Bunton hopes will ultimately enable the app to give individualized health recommendations for every dog. "Even in my house, what my other dog, Monster, needs and what Donovan needs are different," she says.

Bunton is keenly aware of the stigma associated with data collection, and says Whistle's largely Millennial staff of about 60 employees (and eight dogs) constantly weighs in on moral and ethical considerations of issues facing the business. "It's [about] getting clearer vision on the things that matter to our users," she adds. "And you do that through the personal information that they're willing to share with you."

A competitive pack

Whistle says it's "fast approaching" a majority of the industry's market share by units sold. (The company declined to provide unit sales figures.) Still, it faces stiff competition from startups like Kansas City, Missouri-based FitBark, founded in 2013, as well as larger companies like Garmin and Motorola, which both sell pet-monitoring devices and boast financial heft on par with Mars.