An Activity Tracker is a device or application that monitors and records various physical activities, such as walking, running, cycling, and sleeping. These trackers often use sensors to measure metrics like steps taken, distance traveled, calories burned, and heart rate. Many activity trackers can sync with smartphones or computers to provide users with detailed insights into their fitness levels and progress over time. Most activity trackers come in the form of wristbands or smartwatches, and they may include features like GPS tracking and notifications for calls or messages. Popular brands include Fitbit, Garmin, and Apple Watch. Users can set fitness goals and receive reminders to stay active, making it easier to maintain a healthy lifestyle.