| General | |
|---|---|
| Manufacturer | Fourth Frontier |
| Type | ECG-based chest strap heart rate monitor (general wellness product) |
| Series | Frontier |
| Released | 5 October 2026 |
| Price at launch | USD |
| Predecessor | Frontier Zone |
| Successor | Not yet announced |
| Weight | 23g |
Specifications and features as at launch.
Jump to: Expert opinion | What’s new | Specifications | Battery life | Features | Activity profiles | Further reading
Expert opinion
The Frontier X3 keeps the Zone’s ECG-based sensing and vibration alerts but does not let you see, stream or export the ECG trace. Fourth Frontier says it still samples ECG inside the strap to calculate its metrics, and withholds the trace to keep this wellness range separate from the FDA-cleared Frontier X Plus.
Battery life rises to around 4 months of typical use, from around 30 days on the Zone. The strap is screen-free, charges over USB-C and is more breathable than the X2’s. It is sold in the US only. Readers in the UK and Europe can buy the Zone or the X2 from the Fourth Frontier UK store.
Fourth Frontier X3
Screen-free heart rate strap with USB-C charging, US only.
What’s new versus the Frontier Zone
Hardware
- Typical battery life of around 4 months, up from around 30 days
- A more breathable strap
Software
- ECG streaming, display and download are not available, even with Frontier Premium. On the Zone they are part of Premium.
Unchanged
- Pod dimensions of 73.6 x 25.1 x 14mm and no screen
- USB-C charging and IP67 water resistance
- Bluetooth 6.0 and three simultaneous connections
- Continuous recording, 7 days when recording 24 hours a day
- Heart rate, HRV, strain and breathing rate, plus vibration alerts and training load
Specifications
| Physical | |
|---|---|
| Pod dimensions | 73.6 x 25.1 x 14mm |
| Weight | 23g (around 10% lighter than the Frontier X2) |
| On-device screen | None |
| Water rating | IP67 |
| Charging | USB-C |
| Strap | More breathable than the Frontier X2 |
| Sensing | |
| ECG lead | Single-lead ECG, approximating the V5 position of a 12-lead ECG |
| ECG sampling rate | Sampled at 125Hz, stored at 125Hz |
| Movement metrics | Body Shock and step cadence |
| Connectivity | |
| Bluetooth | Bluetooth 6.0 |
| ANT+ | Not supported |
| Simultaneous connections | Three: the app plus two external devices |
| Heart rate streaming to | Apple Watch, Garmin, Whoop, Peloton, Zwift and other BLE fitness devices |
| App connections | Apple Health or Health Connect, Strava and Garmin Connect (Garmin Connect requires Frontier Premium) |
| ECG access | |
| Viewing the ECG trace | Not supported |
| Streaming ECG | Not supported, including with Premium |
| Downloading ECG data | Not supported (no PDF or raw data) |
| Subscription | |
| Frontier Premium adds | VO2 max, ventilatory thresholds, readiness score, sleep staging and Garmin Connect |
| Regulatory | |
| Classification | General wellness product |
| FDA | Not a cleared medical device |
| Where to buy | US store only |
Fourth Frontier’s product comparison document gives 125Hz as the ECG sampling rate. The company’s website has quoted a higher internal figure of 500Hz. This page uses the comparison document.
Battery life
| Mode | Battery life |
|---|---|
| Typical use | Around 4 months |
| Recording continuously, 24 hours a day | 7 days |
The Fourth Frontier website quotes up to 4 months at roughly an hour of use a day, and up to 14 days of continuous use. This page uses the figures in the company’s product comparison document.
Features
Feature explanations are covered in the relevant the5krunner heart rate hub. Features are listed under Fourth Frontier’s own headings.
Performance metrics
- VO2 max trends (requires Frontier Premium)
- Heart rate and HRV
- Cardiac age trends
- Strain monitoring
- Training load
- Body Shock
- Breathing rate
- VT1 to VT2 based zones (requires Frontier Premium)
Activity and alerts
- Tracks 20+ activities, including running, cycling, rowing and hiking
- Zone-based alerts with personalised vibration alerts
- Session metrics: pace, distance and duration
- Activity tagging and notes
Recovery and readiness
- Advanced HRV insight
- Readiness score (requires Frontier Premium)
- Sleep stage analysis: wake, light, deep and REM (requires Frontier Premium)
- Stress monitoring
Connectivity
- Up to three devices connected at once
- GPS via your smartphone
- Works with Garmin, Strava, Coros, Zwift, Peloton and others
Activity profiles
Fourth Frontier says the X3 tracks 20+ activities and names running, cycling, rowing and hiking. The manufacturer’s product page does not list the full set of activity profiles.
Fourth Frontier X3
Screen-free heart rate strap with USB-C charging, US only.
Further reading
- the5krunner Frontier X3 launch and buying guide
- the5krunner Frontier Zone review
- the5krunner Frontier X2 review
- the5krunner Frontier X Plus review
- Fourth Frontier specifications
- Heart rate monitoring hub
Related straps
Looking at alternatives to the Frontier X3?
- Predecessor: Fourth Frontier Zone, the UK and Europe model, which can stream and export ECG with Premium.
- Also consider: the Polar H10. It is hardware only, so you need separate ECG software and it has none of the in-exercise features. It can record an ECG, which makes it competitive on that point.
