Fourth Frontier X3: All you need to know

Fourth Frontier launched the Frontier X3 on 5 October 2026 at $649. It is a screen-free chest strap that turns an ECG signal into training zones, recovery scores and sleep data, and it needs charging only about three times a year. It cannot show you the ECG trace itself, and it is sold in the US only. A full review here will follow later.

Use code LAUNCH30 for 30% off at fourthfrontier.com, which brings the price to $454. The code is a store-wide launch offer as of this writing.

Fourth Frontier X3

Screen-free heart rate strap with USB-C charging, US only.

RRP$649

30% off - use code: LAUNCH30

What Frontier X3 does for your training

The strap reads your heart’s electrical signal to a medical-grade ECG level – for more frequent HR and more accurate data than any watch. The heart rate hub explains why a chest strap is the most dependable sensor for hard sessions.

• Vibration alerts without a phone. The pod buzzes when you leave a heart rate zone, so you can stay in the right effort without looking at a screen.
• Zone 2 pacing from breathing. With Frontier Premium, the strap sets zones from breathing patterns at the first and second ventilatory thresholds. Pacing by ventilatory thresholds avoids the cardiac drift that makes heart rate zones unreliable on long efforts.
• Training load and Body Shock. Training load shows how hard a block has been, and Body Shock tracks the impact your body absorbs on each run.
• Works with your existing kit. It streams heart rate to Garmin, Apple Watch, Whoop, Peloton, Zwift and other Bluetooth devices, and it can connect to three at once. It does not support ANT+.
• Few charging days. Fourth Frontier quotes around 4 months of typical use at about an hour a day. With around-the-clock recording, it lasts 7 days.

What it does for your health picture

Overnight and daily data is where X3 adds most beyond a standard heart rate strap. Fourth Frontier lists heart rate variability, breathing rate, stress monitoring, strain and cardiac age trends. With Frontier Premium, it adds sleep stages (wake, light, deep and REM), a readiness score and VO2 max trends.

These are trend tools. They show whether you are adapting to training or carrying too much stress, and they work best when you read them over weeks rather than days.

What it cannot tell you

Frontier X3 does not display, stream or export the ECG trace. Fourth Frontier says it samples the signal inside the strap to calculate its metrics, and removed the trace “to maintain a clear boundary between medical and non-medical offerings”. It is a general wellness product and is not intended to diagnose, treat, cure or prevent any condition.

There are three practical consequences for a buyer:

• You cannot export a trace to show a doctor after a scare mid-ride. Frontier X2 and Zone can, and the Zone review shows what that trace looks like.
• It does not report rhythm status such as atrial fibrillation. Only the FDA-cleared Frontier X Plus does, and it needs a prescription.
• A reassuring number from a wellness strap is not a clear heart check. Chest pain, fainting or an unusually irregular pulse during exercise needs a doctor, whatever the strap shows. The London Marathon ECG article covers what exercise ECG can and cannot catch.

Risks to weigh before you buy

• It is untested here. I haven’t used Frontier X3 yet. The battery, accuracy and app claims in this article come from Fourth Frontier, and the5krunner review will follow.
• Several of the best features need a subscription. VO2 max, ventilatory zones, readiness, sleep staging and Garmin Connect require Frontier Premium, which the US store lists at about $15 a month. The strap still works without it, but you get only heart rate, HRV, strain, breathing rate, and training load.
• The price is high for a wellness strap. At $649 RRP, Frontier X3 costs far more than a standard chest strap such as the Garmin HRM 600. The ECG signal adds extra metrics, but the trace isn’t available to you.
• It is US only. Fourth Frontier’s UK and Europe store does not sell X3, so UK buyers would have to import it, and I have not confirmed how import costs or warranty support would work.
• Returns and warranty. Fourth Frontier’s other straps carry a 14-day return period and a 1-year warranty. Check the X3 terms at checkout, because I have not confirmed they match.
• The trace-free design is unlikely to change. If you might want an ECG record later, Fourth Frontier has said it is keeping that function for its medical device, so X3 is unlikely to offer it.

Who it suits, and who should look elsewhere

Frontier X3 suits athletes in the US who want a chest strap with recovery and sleep data and who rarely want to charge it. It doesn’t suit anyone buying it for the ECG itself.

• Want the ECG trace and live in the UK or Europe: Frontier Zone, at GBP 179 with code 5KRUNNER (RRP GBP 199).
• Want a screen on the pod and ECG streaming without a subscription: Frontier X2, in my X2 review.
• Have, or are being investigated for, a heart condition: Frontier X Plus, with a prescription.
• Want a cheap ECG recorder: the Polar H10. It is hardware only, needs separate ECG software, and has none of the in-exercise features.

All four straps are compared on the Fourth Frontier specifications page, and the full details for this strap are on the Frontier X3 specifications page.

Fourth Frontier X3

Screen-free heart rate strap with USB-C charging, US only.

RRP$649

30% off - use code: LAUNCH30

Quick answers

Can the Fourth Frontier X3 detect an irregular heartbeat?
No. X3 is a general wellness product and does not report rhythm status or show the ECG trace. Fourth Frontier’s FDA-cleared Frontier X Plus reports atrial fibrillation, bradycardia and tachycardia, and it needs a prescription.

Do I need a subscription for the Fourth Frontier X3?
No, but VO2 max, ventilatory thresholds, a readiness score, sleep staging and Garmin Connect require the optional Frontier Premium subscription. The strap still records heart rate, HRV, strain, breathing rate and training load without it.

How long does the Fourth Frontier X3 battery last?
Fourth Frontier quotes around 4 months of typical use at about an hour a day. At 24 hours of recording a day, it lasts 7 days.

Is the Fourth Frontier X3 worth buying over the Zone?
The X3 lasts around 4 months per charge, compared with around 30 days for the Zone, but it cannot show or export the ECG trace, even with Premium. Zone can with Premium, and it is sold in the UK and Europe at GBP 199 RRP.

Can I buy the Fourth Frontier X3 in the UK?
No. X3 is sold through Fourth Frontier’s US store only. The UK and Europe store sells Frontier Zone and Frontier X2.

How much does the Fourth Frontier X3 cost?
X3 has an RRP of $649. Code LAUNCH30 takes 30% off as of this writing, bringing the price to $454.

Sources and resources

• Fourth Frontier X3 product page
• Frontier X3 specifications

Last Updated on 7 October 2026 by tfk the5krunner

tfk the5krunner

tfk is the founder and author of the5krunner, an independent endurance sports technology publication. With 20 years of hands-on testing of GPS watches and wearables, and competing in triathlons at an international age-group level, tfk provides in-depth expert analysis of fitness technology for serious athletes and endurance sport competitors. ID