The Fitbit Alta Blue Bulk in size Large, model FB406L, is an activity tracker that offers a variety of measurements including heart rate, speed, cadence, time, calories, and distance. It features a rechargeable battery with up to 5 days of battery life, multiple sensors such as accelerometer, gyroscope, GPS, and compass, and is compatible with various operating systems like Windows, iOS, and Android. With its sleek black color and unisex design, this Fitbit Alta is ideal for indoor and outdoor activities like gym training, weight lifting, yoga, and running, providing users with real-time insights to help them achieve their fitness goals.