Fitbit (NYSE: FIT) is an American company headquartered in San Francisco, California, known for its products of the same name, which are activity trackers, wireless-enabled wearable technology devices that measure data such as the number of steps walked, heart rate, quality of sleep, steps climbed, and other personal metrics involved in fitness. The first product released was the Fitbit Tracker. Some evidence has found that the use of similar devices results in less weight loss rather than more.

Alongside the activity trackers, Fitbit offers a website and mobile app for iOS, Android and Windows 10 Mobile. The trackers can be synced to smart devices via Bluetooth or uploaded to a computer running Windows or macOS using the Bluetooth USB dongle. Users have the ability to log their food, activities, and weight, to track over time and can set daily and weekly goals for themselves for steps, calories burned and consumed, and distance walked. Calories in versus calories out is more accurately measured when app users keep their tracker on. However, the app can be used without a tracker to measure calories on a lifestyle app. The app offers a community page where users can challenge themselves and compete against other users. The social element anticipates an increase in motivation, finding that users take an average of 700 more steps per day when they have friends on the app. Users can choose to share their progress pictures and achievement badges.

The company plans to release its Fitbit Ionic smartwatch in October 2017 for $300.

In those who are overweight or obese, a 2016 study indicates that the use of wearable technology combined with standard behavioral weight loss intervention results in less weight loss after two years of use when compared to usual weight loss interventions. There was no evidence that the devices altered the amount that people exercised or their diet compared to control. A 2015 study found use of lifestyle apps demonstrate promising results in promoting healthy living in adults. It is unclear whether these devices affect the amount of physical activity children engage in.

A small 2014 study of eight fit band devices during a 69-minute workouts that included 13 different activities found the bands were at best "reasonably accurate", with the Fitbit Zip and Fitbit One scoring 10.1% and 10.4% error ratings, respectively.

A small 2015 study had participants wear multiple devices on their wrists and hips performing different walking/running speeds on a treadmill. Fitbit devices worn on the hip accurately measured steps taken within 1 step of 100% accuracy. Devices worn on the wrist, however, were off by an average of 11 steps per minute. When measuring the number of calories burned, Fitbit devices worn on the hip underestimated by an average of 6%, while devices worn on the wrist overestimated calories burned by 21%. Authors concluded that both the Fitbit One and Fitbit Flex devices reliably measured step counts and energy expenditure, with hip-based Fitbit devices being more accurate than wrist-based devices. These measurements did not address the question of health effects.

Fitbit, working with the Consumer Protection Safety Commission, recalled the Fitbit Force on February 20, 2014 because some users experienced allergic reactions to the materials used in the product. On March 12, 2014, the Consumer Product Safety Commission (CPSC) made the recall official. At that time, it was revealed that there were 9,900 reports of skin irritation and 250 reports of blistering . The product is no longer for sale on Fitbit's website.

In April 2017, a woman claimed her Fitbit Flex 2 malfunctioned and caught on fire, causing second-degree burns on her arm. Following an investigation, Fitbit is adamant the cause of the exploding tracker was due to external forces, assuring its customers it is not aware of any other complaints and they can confidently wear their own Fitbit with no concerns.

Headquartered in San Francisco, California, Fitbit was founded on May 1, 2007 by James Park (CEO) and Eric Friedman (CTO). On May 7, 2015, Fitbit announced it had filed for IPO with a NYSE listing. The IPO was filed for $358 million. The company's stock began trading with the symbol "FIT" on June 18, 2015. After Fitbit's stocks fell more than 50% in 2016, CEO James Park announced in October that the company was undergoing a major transformation from what he called a "consumer electronics company" to a "digital healthcare company."

On December 7, 2016, Fitbit officially announced that they acquired assets from Pebble, including key personnel, as the company decided to stop producing wearable technology. The acquisition excludes Pebble's hardware products.

In January 2017, Fitbit acquired Romania-based smartwatch startup Vector Watch SRL for $15 million.

Fitbit has won numerous awards, including runner-up at TechCrunch50 in 2008 and Innovation honoree and best in the Health & Wellness category at CES 2009. In 2016, Fitbit ranked 37 out of the 50 most innovative companies for that year. In 2016, the company was ranked #46 on the Deloitte Fast 500 North America list.

To set up and use the hardware, one has to create an account with Fitbit and agree to data collection, transfer and privacy rules.

Starting in June 2011, Fitbit was criticized for its website's default activity-sharing settings, which made users' manually-entered physical activities available for public viewing. All users had the option to make their physical activity information private, but some users were unaware that the information was public by default. One specific issue, which technology blogs made fun of, was that some users were including details about their sex lives in their daily exercise logs, and this information was, by default, publicly available. Fitbit responded to criticism by making all such data private by default and requesting that search engines remove indexed user profile pages from their databases.

The company's devices have also been used in criminal investigations; in one instance, a rape claim against an unnamed intruder was turned around to a criminal charge for false reports based on data from the claimant's Fitbit.

A Fitbit played a role in solving a murder. Connie Dabate was murdered by her husband Richard Dabate. Initially, Richard framed the situation, telling police and law enforcement officials that an intruder had broken into their home and fatally shot his wife. However, Connie’s Fitbit tracker showed that she was at the gym at the time Richard told police his wife was shot. Using Connie’s Fitbit and analyzing her movements, analysts were able to create a timeline that proved Richard had created a false story.

On March 5, 2017, Kelly Herron was using a public bathroom, when a man, who had been convicted of previous sex crimes, attempted to rape Herron. Herron fought her way out of the crime and the story became widely circulated because her Fitbit had tracked her frantic movements during her escape.

On March 10, 2015, Jeannine M. Risley fabricated a story in which an intruder appeared in her employer’s home she was staying at and raped her. Risley told police that a man had assaulted her around midnight. Police found a Fitbit lying on the floor when they arrived at the scene. Prosecutors used the Fitbit as evidence and data to determine what had occurred. The Fitbit revealed that Risley was active throughout the night, and the Fitbit surveillance analysis demonstrated Risley had not gone to bed like she stated to the police; therefore, proving Risley had lied to the police.