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Polar Loop with Keely, or Amazfit Helio Strap.
The Helio Strap and the Polar Loop are both screen-free bands with no subscription. Amazfit’s Zepp app gives the strap BioCharge, an energy score, plus training metrics and blood oxygen, and the strap can vibrate and send its heart rate to other devices. Keely gives the Loop one Recovery score with a published formula, a Load target for the day, live stress, a VO2 max from your walks and runs and Keely Age, and keeps your raw heart data on your iPhone. The Helio Strap is $99.99 and the Helio Strap Pro $199.99; a Polar Loop is $199.99, and Keely is free.
Updated
At a glance
| Polar Loop with Keely | Amazfit Helio Strap and Strap Pro | |
|---|---|---|
| Price (US) | $199.99 for the Loop, once. Keely is free | Helio Strap $99.99 (sold out in Amazfit’s US store on October 5, 2026); Helio Strap Pro $199.99 |
| Subscription | None | None required. Zepp Aura, an optional add-on for sleep and stress, is paid |
| Morning | Recovery, 0–100 %: HRV, resting heart rate, sleep, breathing rate and skin temperature | BioCharge, an energy score from sleep, naps, exertion and stress. The Pro lists HybridCharge as well |
| Training | Load: points per minute by heart-rate zone, no ceiling, with a target range each morning | VO2 max, training load, training effect and recovery time, and PAI |
| Stress | Live, 0–100, scored only while you’re still | Stress level |
| Sleep | Stages from the Loop, need (goal, debt and a hard day), consistency and a lights-out time | Sleep stages with REM, sleep HRV and a sleep score |
| Sensors | Optical heart rate, accelerometer, skin temperature | Optical heart rate, accelerometer, gyroscope, temperature and blood oxygen |
| Vibration | None: the Loop can’t vibrate | A vibration motor |
| Battery, by the maker | Up to 8 days (Polar’s figure, with Polar Flow) | Up to 10 days (Pro: 11) |
| Worn | On the wrist | On the wrist or the upper arm |
| Phones | iPhone | iPhone and Android |
| Formulas | Every input, weight and constant is published | Inputs are described by Amazfit |
| Your data | Raw heart data stays on your iPhone; your account backs up daily summaries | In your Zepp account; workouts go to Strava, TrainingPeaks, komoot, Apple Health and others |
Facts about Amazfit come from Amazfit’s and Zepp’s own pages, checked October 5, 2026. This page compares cost, scores and data; it doesn’t test sensor accuracy.
Where Amazfit does more
- It can vibrate. Both straps have a vibration motor. The Loop has none.
- A training sensor. Upper-arm wear, 50+ sports modes, recognition of 25 strength movements, a HYROX race mode, up to 21 days of heart rate stored offline, and heart rate sent to watches, bike computers, gym equipment and apps.
- Blood oxygen, and the quality of your breathing in sleep.
- Workouts out. Strava, adidas Running, TrainingPeaks, komoot, Relive, Google Fit and Apple Health. Keely doesn’t export yet.
- Android as well as iPhone. Keely is iPhone only.
- It costs less, when the original is in stock: $99.99.
Where Keely is different
- One morning score, explained. Recovery is a single number from 0 to 100 %, and tapping it shows each input as helping, holding back or normal. Its weights are on the methodology page.
- A Load target each morning. Keely counts every minute by its heart-rate zone, with no ceiling, and sets a range for the day from your Recovery and your last four weeks. See Load.
- Stress as a number, live. From 0 to 100 while Keely is open, and never scored while you move. See Stress.
- VO2 max from effort, and Keely Age. Keely reads the pace of your steady walks and runs against the Loop’s heart rate, shows the likely range, and turns it into years each Monday. See Fitness and Keely Age.
- Your raw heart data stays on your iPhone. Only daily summaries are backed up to your account.
Frequently asked questions
Is the Polar Loop with Keely an Amazfit Helio Strap alternative?
Both are screen-free bands with no subscription. The Helio Strap is built as a training sensor, with upper-arm wear and heart rate sent to other devices; the Loop with Keely is built around one morning Recovery score, a daily Load target and live stress, with every formula published.
Does the Helio Strap need a subscription?
No, by Amazfit’s own FAQ. Zepp Aura, a paid add-on for sleep and stress, is optional.
Can I use a Helio Strap with Keely?
No. Keely works with the Polar Loop.
Sources
- Helio Strap: Amazfit’s US store and launch announcement (June 24, 2025).
- Helio Strap Pro: Amazfit’s US store. HybridCharge: Zepp’s announcement (June 2, 2026).
- Zepp Aura: Amazfit’s US store. The Zepp app: the App Store.
- Polar Loop price: Polar’s US store. Specifications: Polar Loop user manual.
All checked October 5, 2026. Prices and features change, so check Amazfit’s before you buy. Amazfit, Helio, Zepp and BioCharge are trademarks of Zepp Health; Keely isn’t affiliated with or endorsed by Zepp Health or Polar.
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