Top pickFitbit
Fitbit Charge 6 Fitness Tracker
- Built-in GPS with real-time pace
- 7-day battery (5-6 hours with GPS active)
Fitness Trackers Buying Guide: Specs, Sensors, and What Actually Matters
A fitness trackers buying guide covering what heart rate sensors, SpO2, water resistance ratings, and battery specs actually mean in practice, so you can read a spec sheet and know what it translates
- BuyOnceRight Research Desk
- Updated
- 3 min read
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Water Resistance: ATM Explained
An ATM rating measures pressure tolerance, not literal swimming depth.
A 5 ATM rating, standard across the Fitbit Charge 6, Garmin Vivosmart 5, Amazfit Band 7, and Samsung Galaxy Fit3, covers pool swimming, showering, and rain without concern.
Trackers rated only for splash resistance should stay dry beyond incidental contact.
Heart Rate Sensors: Optical vs ECG
Optical heart rate sensors, the standard on every tracker in this category, use light to detect blood flow continuously through the day.
They're accurate for steady-state activity but lag during rapid intensity changes.
ECG, found on some higher-end smartwatches but not the trackers covered here, adds a spot-check electrical reading that can flag specific rhythm irregularities more precisely.
Battery Life: Rated vs Real-World
Manufacturer battery ratings assume light, typical use.
GPS-active tracking and always-on display settings both cut battery life meaningfully:
Subscription Costs Hidden in the Price
Not every feature advertised on the box is included in the purchase price.
Fitbit's Charge 6 requires a Premium subscription for its Daily Readiness Score and detailed sleep trend history.
Garmin's Vivosmart 5, Amazfit's Band 7, and Samsung's Galaxy Fit3 all include their full feature sets with no subscription required.
Platform Compatibility
Check this before comparing anything else.
The Samsung Galaxy Fit3 requires Android and has no iOS app.
The Fitbit Charge 6, Garmin Vivosmart 5, and Amazfit Band 7 all support both iOS and Android.
See Also
How to Choose a Fitness Tracker, a decision framework Fitness Tracker Inaccurate Heart Rate Readings, troubleshooting sensor accuracy Fitness Tracker Draining Battery Fast, troubleshooting battery issues
Put it into practice
Top fitness trackers we recommend
- Garmin
Garmin Vivosmart 5
- Large, readable touchscreen with adjustable text size
- Irregular heart rhythm notifications
Answers
Frequently asked questions
What does ATM water resistance mean on a fitness tracker?
ATM stands for atmosphere, a unit of pressure roughly equivalent to being submerged 10 meters underwater. A 5 ATM rating, common on trackers like the Fitbit Charge 6, Garmin Vivosmart 5, Amazfit Band 7, and Samsung Galaxy Fit3, means the device isto withstand pressure equivalent to 50 meters depth, well beyond what pool swimming or showering produces. It's not a literal depth rating for diving, it's a pressure tolerance standard.
What's the difference between optical heart rate and ECG on a fitness tracker?
Optical heart rate uses light sensors (usually green LEDs) on the back of the tracker to detect blood flow changes through the skin, providing continuous background heart rate readings. ECG (electrocardiogram) uses electrical sensors, typically requiring you to touch the device with your other hand for a spot reading, and can detect specific irregular rhythm patterns like atrial fibrillation more precisely than optical sensors alone. Most fitness trackers in this category rely primarily on optical sensors for continuous tracking.
Does a higher price always mean better sensor accuracy?
Not necessarily for basic metrics. Higher prices generally buy built-in GPS, more advanced software features, and better display quality rather than dramatically better raw sensor accuracy.
How often should I replace a fitness tracker?
Most fitness trackers remain functionally accurate for 2 to 4 years, with battery capacity typically the first component to degrade noticeably, extending charge cycles shorter over time. Band material and clasps on budget trackers tend to show wear before the electronics themselves fail. There's no fixed replacement schedule, replace it when battery life or sensor performance no longer meets your needs, or when a meaningful feature upgrade becomes available.
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