The term “activity trackers” now primarily refers to wearable devices that monitor and record a person's fitness activity. The concept grew out of written logs that led to spreadsheet-style computer logs in which entries were made manually, such as that provided in the US by the President's Council on Physical Fitness and Sports as part of The President's Challenge.[2] Improvements in technology in the late 20th and early 21st century allow automating the monitoring and recording of fitness activities and integrating them into more easily worn equipment. Early examples include wristwatch-sized bicycle computers that monitored speed, duration, distance, etc., available at least by the early 1990s. Wearable heart rate monitors for athletes were available in 1981.[3] Wearable fitness tracking devices, including wireless heart rate monitoring that integrated with commercial-grade fitness equipment found in gyms, were available in consumer-grade electronics by at least the early 2000s. Wearable fitness tracking computers with tightly integrated fitness training and planning software were available as consumer products by at least 2006.

Electronic activity trackers are fundamentally upgraded versions of pedometers; in addition to counting steps, they use accelerometers and altimeters to calculate mileage, graph overall physical activity, calculate calorie expenditure, and in some cases also monitor and graph heart rate and quality of sleep.[5][6][7] Some also include a silent alarm.[6][8] Some newer models approach the US definition of a Class II medical monitor, and some manufacturers hope to eventually make them capable of alerting to a medical problem, although FDA approval would be required.[9] Early versions such as the original Fitbit (2009), were worn clipped to the waist;[5] formats have since diversified to include wristbands and armbands (smart bands) and smaller devices that can be clipped wherever preferred.[8][10] Apple and Nike together developed the Nike+iPod, a sensor-equipped shoe that worked with an iPod Nano.

In addition, logging apps exist for smartphones and Facebook;[7] the Nike+ system now works without the shoe sensor, through the GPS unit in the phone. The Apple Watch and some other smart watches offer activity tracker functions.[9] In the US, BodyMedia has developed a disposable activity tracker to be worn for a week, which is aimed at medical and insurance providers and employers seeking to measure employees' fitness,[11] and Jawbone's UP for Groups aggregates and anonymizes data from the company's wearable activity trackers and apps for employers.[12] Other activity trackers are intended to monitor vital signs in the elderly, epileptics, and people with sleep disorders and alert a caregiver to a problem.[9]

Earbuds and headphones are a better location for measuring some data, including core body temperature; Valencell has developed sensor technology for new activity trackers that take their readings at the ear rather than the wrist, arm, or waist.

There are collar-mounted activity trackers for dogs.

Much of the appeal of activity trackers that makes them effective tools in increasing personal fitness comes from their making it into a game, and from the social dimension of sharing via social media and resulting rivalry.[5][7][17][18] The device can serve as a means of identification with a community,[19] which extends to broader participation.

The standard activity-tracking smartphone or web apps present data in statistical form meant to be viewed after the activity has ended. However, research suggests that if we want a richer understanding of the data, we need intelligent computing to be included in the systems that run the apps.[20]

Some users and reviewers remain ambivalent towards the technology, making the point that in such a “mirror” displaying one's identity, misrepresentations are problematic.[21] All forms of lifelogging also carry privacy implications.[22] Social networks associated with activity trackers have led to breaches of privacy such as involuntary publication of sexual activity,[23] and the potential for advertisers and health insurers to access private health data through the devices is a concern.[9]

Wearable sensors have been widely used in medical sciences, sports and security. Wearable sensors can detect abnormal and unforeseen situations, and monitor physiological parameters and symptoms through these trackers. This technology has transformed healthcare by allowing continuous monitoring of patients without hospitalization. Medical monitoring of patients’ body temperature, heart rate, brain activity, muscle motion and other critical data can be delivered through these trackers. Moreover, in sports training there is an increasing demand for wearable sensors. For example, measurement of sweat rate was possible only in laboratory based systems a few years ago, but is now possible using wearable sensors.[24]

Activity trackers are available both with and without display

Certain movements of the user, such as working in the household, cycling, swimming, dancing or rowing can distort the results obtained from activity trackers. In a test of Stiftung Warentest, for example, no product determined even approximately the distance of a bike ride. Furthermore, the determined values for the human energy transformation are erroneous.[26] With the heart rate large deviations have been observed at wristlet trackers, and it is recommended for this purpose to use appropriate chest straps.[26]

Wristbands can be uncomfortable to wear and inadvertently being lost. For some products genotoxic substances were detected.[26]

The connection of activity trackers with social networks can lead to violation of privacy, such as involuntary publication of sexual activity.[27] The apps of some activity trackers not only transmit personal data, but also private address lists to servers on the Internet without notifying or asking the user.[26]

• Basis (owned by Intel) - Basis Carbon Steel Edition
• Bomdic - Gomore
• Fitbit - Fitbit Flex, Fitbit One, Fitbit Zip, Fitbit Surge, Fitbit Charge (replacement for Fitbit Force, which was recalled because some users experienced skin irritation), Fitbit Charge HR, Fitbit Blaze
• Fossil Group - Fossil Q Wearables
• Garmin - Garmin Vivofit, Garmin Vivofit 2, Garmin Vivosmart, Garmin Vivoactive, Garmin Vivosmart HR
• Huawei - Huawei Talkband B1[28]
• I Measure U
• Jawbone - Jawbone UP, Jawbone UP2, Jawbone UP3, Jawbone UP4
• LG Electronics - LifeBand Touch[29] and heart-monitoring headphones[30]
• Medisana - Vifit connect[26]
• Microsoft - Microsoft Band[31]
• Mio Technology - Fuse[26]
• Misfit Wearables - Misfit Shine, Misfit Flash, Beddit
• Nike - Nike+ FuelBand and Nike+ FuelBand SE
• Pivotal Corporation - Pivotal Tracker 1[32]
• Polar Electro - Polar Loop
• Razer - Nabu
• Runtastic
• Samsung - Samsung Gear Fit[29]
• Sony - Sony SmartBand SWR10,[33] Sony SmartBand Talk SWR30[34]
• Spire - Spire
• Withings - Withings Pulse O2, Withings Pulse
• Nudge: an app dashboard for activity trackers[35]
• Xiaomi: Xiaomi Mi Band[36]
• Cooey - Smart blood pressure monitor, scale and glucometer devices
• oDrive Multi-Tracking Physical Challenges monitor
• Apple Watch By Apple
• Moov Now By Moov

• Actigraphy
• eHealth
• Internet of Things
• Quantified self, movement to record, analyze, and improve one's daily life
• Smartwatch
• Wearable computer