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Shadow grey aluminium smartwatch with silicone band, square AMOLED display

Fitbit

Fitbit Sense 2 FB521BKGB-US Shadow Grey Graphite Aluminium smart watch

SKU CH-65RS-9WEQB MPN FB521BKGB-US

Tracks health, stress and sleep with ECG, SpO2 and cEDA sensors, offers six-plus day battery and includes both band sizes

  • ColorShadow Grey
  • TypeSmart Watch
  • Case MaterialAluminium
  • Band MaterialSilicone
  • Band LengthBoth small and large sizes included in box. Small: Fits wris
  • Display TechnologyAMOLED

Color Shadow Grey

  • 6+ days battery life with 12-minute quick charge
  • cEDA sensor tracks body response for stress management
  • ECG app checks heart rhythm from your wrist
  • Built-in Amazon Alexa handles alarms and weather hands-free
  • Contactless payments let you pay directly from the watch

Fitbit Sense 2 Shadow Grey smartwatch

The Fitbit Sense 2 is a health-focused smartwatch with a Shadow Grey aluminium case and AMOLED display. It tracks heart rate, skin conductance and ECG data for adults who want continuous wellness monitoring. Both small and large silicone bands are included to fit wrists from 5.1 to 8.6 inches. The watch stores seven days of detailed motion data on the device.

Compatibility and account requirements

A Google account is required to activate the watch and the Fitbit app must be installed on a compatible smartphone. The ECG app and irregular rhythm notifications are only available in select countries and are not intended for people under 22 years old. SpO2 tracking and Health Metrics dashboard access also vary by region and may require a Fitbit Premium membership.

Battery life and charging

Battery life reaches 6+ days under typical use, though always-on display, SpO2 and the cEDA sensor reduce that figure. A full day of charge can be added in 12 minutes using the supplied cable. The case measures 0.44 in thick and weighs 0.08 lb, so it remains light during continuous wear.

Highlights

  • 6+ days battery life with 12-minute quick charge
  • cEDA sensor tracks body response for stress management
  • ECG app checks heart rhythm from your wrist
  • Built-in Amazon Alexa handles alarms and weather hands-free
  • Contactless payments let you pay directly from the watch

Specifications

BrandFitbit
ModelSense 2
Part NumberFB521SRWT-US
ColorShadow Grey
TypeSmart Watch
Case MaterialAluminium
Band MaterialSilicone
Band LengthBoth small and large sizes included in box.
Small: Fits wrist 5.1 - 7 inches in circumference
Large: Fits wrist 6.5 - 8.6 inches in circumference
Display TechnologyAMOLED
Built-in StorageSaves 7 days of detailed motion data, minute by minute
Battery LifeBattery life of 6+ days. Battery life and charge cycles vary with use, settings and other factors; actual results will vary. Use of the always-on display, SpO2 and the cEDA sensor will require more frequent charging. Up to 5 hours with continuous GPS. We recommend charging your tracker every few days to ensure you are always tracking.
SpecificationRequirements:
Google account will be required.
The Fitbit app is compatible with most popular phones. To set up and use your Fitbit products and services, you must install the Fitbit app on a compatible device running one of the following operating systems:
Apple iOS 15 or higher.
Android OS 10 or higher. See additional tips for Android phones here.
Syncing range: Up to 30ft
Certain features like smartphone notifications may require Android 10+.
Syncing requires Bluetooth® LE, an internet connection and location permissions granted on the phone
FeaturesMulti-path optical heart rate sensor
Electrical sensor to measure skin conductance (cEDA) for body response tracking
Multipurpose electrical sensors compatible with ECG app & EDA app. ECG not available in all countries.
Red and infrared sensors for oxygen saturation (SpO2) monitoring. Not available in all countries. Not intended to diagnose or treat any medical condition or for any other medical purpose. Intended to help you manage your well-being and keep track of your information. Requires more frequent charging.
Gyroscope
Altimeter
3-axis accelerometer
Skin temperature sensor. Onl
HeightHeight: 0.44 in (11.2 mm)
WidthWidth: 1.59 in (40.5 mm)
DepthLength: 1.59 in (40.5 mm)
Weight0.08 lb (37.64 g)
Package ContentFitbit Sense 2
Classic band (small & large)
Charging cable
Shipping weight0.19 kg
Package size51 × 51 × 25 mm

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Questions about this item

What bands and accessories come in the box and is anything else needed to start using it?

The box contains the Sense 2 watch, a classic silicone band in both small (5.1‑7 in) and large (6.5‑8.6 in) sizes, and a charging cable. A Google account and the Fitbit app on a compatible phone are required for setup.

Which band size should I choose for my wrist circumference?

The small band fits wrists from 5.1 to 7 inches around; the large band fits 6.5 to 8.6 inches. Both sizes are included, so you can swap to the one that feels secure and comfortable.

What does the 6+ day battery claim mean when I use always‑on display, SpO2 and the cEDA sensor?

The 6+ day figure is a baseline; enabling always‑on display, SpO2 tracking or the cEDA body‑response sensor will reduce runtime and require more frequent charging. A 12‑minute charge adds a full day of use.

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