Apple Watch Series 2Fitbit Blaze
Tech specs 
Size38.6mm x 33.3mm x 10.5mm (H x W x D)
32.0mm x 35.9mm x 10.5mm (H x W x D)
Width 40mm
(Sizes depend on type of band)
MaterialSteel, Aluminum, Ceramic, Sapphire CrystalStainless steel clasp, Classic band (elastomer), Metal band (stainless steel metal), Leather band (soft, genuine leather)
Charginginductive chargingUSB
BatteryLithium-ionLithium-polymer
Battery life18+ hoursup to 5 days
Water-resistance5 ATM (50 metres)Sweat, rain and splash proof.
Weight25 grams to 69 grams depending on the model43 grams
SensorAmbient light, Heart rate sensor, accelerometer, gyroscope, built-in gps.3-axis accelerometer, 3-axis gyroscope, Optical heart rate monitor, Altimeter, Ambient light sensor and Vibration motor
DisplayOLED Retina display with Force Touch
Ion-X glass (strengthened glass)
Touch-screen colour LCD.
Screen size38mm: 340x272 pixels
42mm: 390x312 pixels
19.05mm x 25.4mm
ColorsGold, Rose Gold, Space Gray, Silver, Black. Straps vary by editions.Classic (Black, Blue and Plum), Leather (Black, Camel and Mist Gray), Metal
OtherPLATFORM: watchOS
PROCESSOR: Apple S2, dual-core
MEMORY: 512 RAM, 8GB storage (2GB of which can be used for music)
CONNECTIVITY: Bluetooth 4.0, NFC, WiFi
Activity tracking 
StepsYesYes
DistanceYesYes
Calories burnedYesYes
ActivityYesYes
FloorsYes
SleepYes
Heart rateYes24/7
Stress & recovery
Pulse Ox
Respiration rate
UV exposure
Skin temperature
Galvanic skin response
Hydration level
Calorie intake
GPSYesConnected 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 Guided breathing, music control.
Non-fitness functions 
Smartphone notificationsYesYes
On-board music storageYes
Connected payYes
LTE
Links 
Affiliate link*AmazonAmazon | Fitbit
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