Fitbit Charge 3Garmin Vivosmart 4
Tech specs 
SizeDevice Dimensions: 35.8mm x 22.7mm x 11.8
One size (small and large bands included)
Width: 15mm
Depth: 10.5mm
Small/medium: 15 x 10.5 x 197 mm (fits wrists with a circumference of 122-188 mm)
Large: 15 x 10.5 x 223 mm (fits wrists with a circumference of 148-215 mm)
MaterialBuilt of more lightweight material including an aerospace grade aluminum case and Corning Gorilla Glass 3 display. The housing and buckle are made of anodized aluminum.Polycarbonate lens, aluminium bezel, silicone strap
ChargingUSBUSB
BatteryLithium-polymerLithium battery
Battery lifeup to 7 daysUp to 7 days
Water-resistance5 ATMUp to 50 metres (5 ATM)
Weight29 gramsSmall/medium: 16.5 g
Large: 17.1 g
SensorOptical heart rate tracker, 3-axis accelerometer, altimeter, SpO2, vibration motor3 axis-accelerometer, barometric altimeter, heart rate monitor, vibration alert, ambient light sensor, Pulse Ox
DisplayOLED full touchscreen, TFTOLED
Screen size35.8mm x 22.7mm0.26" x 0.70" (6.6 mm x 17.7 mm), 48x128 pixels
ColorsMultipleVarious
OtherNFC (Special edition)
Connectivity: Bluetooth, WiFi
Charge 3 stores your stats and data for 7 days in between the times you sync your tracker.
Activity tracking 
StepsYesYes
DistanceYesYes
Calories burnedYesYes
ActivityYesYes
FloorsYesYes
SleepYesYes
Heart rate24/7 + HRV (premium subscription)24/7
Stress & recoveryYes
Pulse OxYesYes
Respiration rateYes (premium subscription)
UV exposure
Skin temperature
Galvanic skin response
Hydration level
Calorie intake
GPSConnected GPSConnected GPS
Running featuresAccelerometer (calculates distance for indoor workouts, without need for a foot pod), personal records.
Swimming features
Other Guided breathing, Female Health Tracking- Body Battery™ Energy Monitor
- automatic rep count in the gym
- Clock, music control, auto goal, move bar
Non-fitness functions 
Smartphone notificationsYesYes
On-board music storage
Connected payYes (special edition)
LTE
Links 
Affiliate link*Amazon | FitbitAmazon | Garmin
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