Frontier X3 launches as a lighter chest strap with four-month battery life

Fourth Frontier has launched the Frontier X3, with much longer battery life, lighter hardware and a bigger focus on training and recovery. Interestingly, the company has removed access to the raw ECG signal, even though ECG still sits at the heart of how the device works.

I have used Fourth Frontier devices for years, including the Frontier X2 and, more recently, the Frontier Zone. The X3 looks like the natural next step at first glance, but this is actually a fairly substantial change in direction.

Battery life takes a huge step forward

A big hardware upgrade is battery life. Fourth Frontier says the X3 can last up to four months if you record around one hour per day, or up to 14 days when recording continuously. So you can, pretty much, forget about charging. These figures put it well ahead of the X2.

Charging has also moved to USB-C, with a full charge taking around an hour. The device weighs 23 grams, around 10% less than the X2, and Fourth Frontier has removed the small display entirely.

That last change probably will not bother many people. I never found the X2 display particularly important, and I said much the same thing when testing the screen-free Frontier Zone. Once the sensor is strapped to your chest, there is not much reason to look at it.

The X3 also moves to Bluetooth 6.0 and supports three simultaneous connections, one phone and two external devices. Fourth Frontier lists compatibility with Garmin, Apple Watch, Zwift, Peloton, Wahoo, Strava and TrainingPeaks, among others. There is still no ANT+ and no built-in GPS, so location data needs to come from another device.

The ECG is still there, but hidden

The Frontier X3 still contains a single-lead ECG sensor and samples the signal internally at 500 Hz. Fourth Frontier uses that electrical signal to calculate heart rate, HRV, breathing rate, Strain and other metrics. But X3 owners cannot see the raw ECG.

That is a notable departure from the Frontier X2, where live ECG viewing and post-workout ECG analysis were a big part of the package. Fourth Frontier says it now wants a clearer separation between its wellness products and medical products, with raw ECG functionality reserved for its Frontier X Plus.

It also produces a slightly odd situation with the cheaper Frontier Zone. Zone still supports continuous ECG recording, with live ECG viewing and ECG exports available through Frontier Premium.

So X3 is not simply a better version of everything that came before it. If you specifically want to inspect your ECG during or after exercise, the X2 or Zone may actually suit you better.

More of a training wearable now

The flip side is that Fourth Frontier is pushing the X3 much harder as a training and recovery device. The device keeps tabs on heart rate, HRV, breathing rate, Strain, Training Load, Body Shock and Cardiac Age, as well as a few other metrics.

There are vibration alerts which can tell you when you move outside selected heart rate, breathing rate or Strain ranges. Those alerts worked well when I tested Frontier Zone. For an easy run, for example, I could adjust my pace from the vibration feedback to stay in Zone 2, without constantly checking my watch.

Frontier Premium also packs VO2 Max analysis, VT1 and VT2 ventilatory threshold zones, Readiness Score and sleep-stage tracking. The latter breaks sleep into Wake, Light, Deep and REM stages, although sleeping every night with a chest strap will probably remain a niche choice compared with a watch or smart ring.

Price and availability

The Frontier X3 costs a rather pricey $649 in the US. However, Fourth Frontier is currently offering 30% off with its LAUNCH30 code.

For existing X2 owners, I would not call this an automatic upgrade. The X3 is lighter, lasts dramatically longer and has better connectivity, but it also gives up one of the features that made the earlier Frontier devices unusual.

For everyone else, the X3 makes more sense due to the upgraded design, much longer battery life and newer connectivity. I’ll be putting that to the test and posting a full review of the X3 in the next few weeks. So keep an eye out for that.