Frontier X2 review: the heart rate monitor I actually prefer using

The Frontier X2 heart rate monitor from Fourth Frontier offers a more modern approach to monitoring heart rate, with a USB-chargeable device, a screen, and a button to manually start a workout and receive haptic feedback. The device's app and USB charging make workout preparation and phone connection easier compared to Polar's offering, which has connectivity issues and a cluttered app.

The Frontier X2 also calculates Whoop-style metrics such as Strain score, Stress score, Heart Rate Variability (HRV), Breathing Rate, and estimates calories burned. While the last metric is outdated, as research shows that calorie estimates based on heart rate are unreliable. An optional premium tier subscription costs $119.99 / £109.99 per year and adds a Readiness score, VO2 Max, and even sleep stage analysis.

The device's continuous ECG can livestream an ECG scan for the user or a medical professional, making it useful for spotting irregular heart rate rhythms over time. The Frontier X2 was tested against the Apple Watch Ultra 4, the Garmin Fenix 9 Pro, and the Polar H10, and the results showed excellent accuracy. The device can be purchased for $599 / £449 / AU$775, and while it is expensive, it addresses some of Polar's pain points, such as a micro-USB charger and a screen for an easier indicator of connection.