Fitbit Flex
Tech specs 
SizeSmall size fits wrists 14cm-16.5cm
Large size fits wrists 16.5cm-21cm
MaterialStainless steel casing, elastomer strap
ChargingUSB
BatteryLithium-polymer
Battery life5 days
Water-resistanceWater resistant up to 10 meters (1 ATM)
Weight10 grams
Sensor3-axis accelerometer, Vibration motor
DisplayFive white LED indicator lights
Screen sizeN/A
ColorsBlack, Slate, Tangerine, Teal, Navy, Violet, Blue, Lime, Pink, Red
Other
Activity tracking 
StepsYes
DistanceYes
Calories burnedYes
ActivityYes
Floors
SleepYes
Heart rate
Vo2Max
Stress & recovery
UV exposure
Skin temperature
Galvanic skin response
Hydration level
Calorie intake
GPS
Running features
Swimming features
Other Auto sleep detection, silent wake alarm
Non-fitness functions 
Smartphone notifications
On-board music storage
Connected pay
Links 
Affiliate link*Amazon | Fitbit
Read moreArticle
*Disclosure: We are a professional review site that receives a small commission from sales of certain items, but the price is the same for you. See our affiliate disclosure page for more details.
**All tech specs and images on this page come from manufacturers. These may change over time as manufacturers sometimes update their devices. While we cannot guarantee absolute accuracy of information on this page, we promise to review this content regularly and do our best to bring you the most up-to-date information. To be absolutely sure of tech specs of a particular device, we recommend checking the manufacturer’s website.