Apple Watch Series 4Fitbit Charge 3
Tech specs 
Size40 mm (band fits 130-200mm wrists)
44 mm (band fits 140-210mm wrists)
Device Dimensions: 35.8mm x 22.7mm x 11.8
One size (small and large bands included)
MaterialSapphire crystal and ceramic back.Built 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.
ChargingWireless chargingUSB
BatteryLithium-ionLithium-polymer
Battery life18+ hoursup to 7 days
Water-resistance5 ATM (50 metres)5 ATM
WeightCase weight: 30.1g (for 40mm version); 36.7g (for 44mm version)29 grams
SensorAmbient light, optical heart rate sensor, Electrical heart sensor, improved accelerometer up to 32 g‑forces, improved gyroscope, GPS (GLONASS, Galileo, and QZSS), barometric altimeter, ambient light sensorOptical heart rate tracker, 3-axis accelerometer, altimeter, SpO2, vibration motor
DisplayLTPO OLED Retina display with Force Touch (1000 nits), Ion-X strengthened glassOLED full touchscreen, TFT
Screen size44mm: 977 sq mm display area (368 x 448 pixel resolution)
40mm: 759 sq mm display area (324 x 394 pixel resolution)
35.8mm x 22.7mm
ColorsA number of aluminum finishes anodized in silver, gold and space gray. You can also pick up the device in gold stainless steel with a matching Milanese band, joining the silver and space black stainless steel models.Multiple
OtherPLATFORM: watchOS
PROCESSOR: S4 with 64-bit dual-core processor, W3 Apple wireless chip
MEMORY: 512 RAM, 16GB storage
CONNECTIVITY: Bluetooth 4.0, NFC, WiFi, LTE and UMTS cellular radio
NFC (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 rateYes24/7 + HRV (premium subscription)
Stress & recovery
Pulse OxYes
Respiration rateYes (premium subscription)
UV exposure
Skin temperature
Galvanic skin response
Hydration level
Calorie intake
GPSYes (GPS,GLONASS, Galileo, and QZSS)Connected GPS
Running featuresWatch displays up to 5 metrics during your run (time, distance, current pace and average pace, heart rate, active calories or total calories).
Swimming featuresPool swim and open water swim. At the end of a swim, the watch displays the time of day the activity took place, dominant stroke used (auto-detection is used), distance, workout time, pool length, laps completed, average pace, average heart rate, and both active and total calories burned, as well as the weather at your location.
Other - ECG monitor
- irregular heart rate detection
- low or high heart rate alerts
- fall detection
Guided breathing, Female Health Tracking
Non-fitness functions 
Smartphone notificationsYesYes
On-board music storageYes (Stream Apple Music direct to watch)
Connected payYesYes (special edition)
LTEYes
Links 
Affiliate link*AmazonAmazon
Read moreArticleReview
*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.