Water Resistance: ATM Explained
An ATM rating measures pressure tolerance, not literal swimming depth.
A 5 ATM rating, standard across the Fitbit Charge 6, Garm in Vivosmart 5, Amazfit Band 7, and Samsung Galaxy Fit3, covers pool swimming, showering, and ra in 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.
Our picks
Products we recommend
As an Amazon Associate I earn from qualifying purchases. Picks are based on manufacturer specs, independent reviews and owner reports.
Top pickFitbit
Built-in GPS means no phone required for accurate route and pace tracking
- Built-in GPS with real-time pace
- 7-day battery (5-6 hours with GPS active)
- Google Maps and Wallet integration
- 40+ exercise modes with automatic recognition
- 50-meter water resistance
✓ Pros
- Built-in GPS means no phone required for accurate route and pace tracking
- Heart rate accuracy improved noticeably over the Charge 5 in steady-state runs
- Daily Readiness Score gives a useful go or rest signal after hard training days
- Fitbit's app remains the most polished for visualizing weekly running trends
✕ Cons
- GPS running continuously cuts battery life to 5-6 hours from the rated 7 days
- Most advanced metrics require a Fitbit Premium subscription
- Screen is small for checking pace mid-stride compared to a running watch
Garmin
Body Battery gives runners a clear number for how much they have left to tra in on
- Body Battery energy monitoring
- Connected GPS via phone
- Up to 7 days battery life
- Animated on-screen workouts
- No subscription required
✓ Pros
- Body Battery gives runners a clear number for how much they have left to tra in on
- No subscription needed to unlock any feature, unlike Fitbit or Whoop
- Comfortable, low-profile band that most testers forget they're wearing overnight
- Battery consistently lasts a full week of daily runs with connected GPS
✕ Cons
- No built-in GPS, so accurate route tracking requires carrying a phone
- Touchscreen can misregister taps mid-run when sweaty
- Smaller third-party app ecosystem than Fitbit or Garmin's own watch line
Amazfit
18-day battery means far fewer mid-training-block charging interruptions
- 18-day battery life
- 1.47-inch AMOLED display
- 120 sports modes
- Alexa built-in
- 5 ATM water resistance
✓ Pros
- 18-day battery means far fewer mid-training-block charging interruptions
- AMOLED display is bright and legible in direct outdoor sunlight
- 120 sports modes cover running, trail running, and treadmill separately
✕ Cons
- Connected GPS only, so a phone is required for accurate route mapping
- Zepp companion app is less polished than Fitbit's or Garm in Connect
- Band material shows wear faster than pricier competitors after months of sweat
FAQ
Common 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, Garm in 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 rema in 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.
Keep researching
Related guides & comparisons
Buying guideGarmin Vivosmart 5Specs, rankings & alternativesSponsored link · confirm price and availability on Amazon · updated October 16, 2026.Buying guideAmazfit Band 7Specs, rankings & alternativesSponsored link · confirm price and availability on Amazon · updated October 16, 2026.Buying guideSamsung Galaxy Fit3Specs, rankings & alternativesSponsored link · confirm price and availability on Amazon · updated October 16, 2026.Best picksBest Fitness Trackers for Running: Top Picks for Pace, Distance, and RecoveryOur top pick for fitness trackers for running is the Fitbit Charge 6 Fitness Tracker (for running).Best picksBest Fitness Trackers for Seniors: Simple, Comfortable, and Easy to ReadOur top pick for fitness trackers for seniors is the Garm in Vivosmart 5 (for seniors). 
