Fourth Frontier is a health and fitness technology company focused on continuous heart monitoring. Its Frontier X2 is worn on a chest strap during exercise, rest or sleep. It records heart and breathing signals and provides live feedback for people seeking detailed cardiovascular data.

How it works
Electrodes against the chest measure the electrical activity controlling each heartbeat, creating a continuous single channel electrocardiogram. Motion sensors add cadence and impact, while software estimates heart rate, heart rate variability, breathing rate, training load and strain. The device can vibrate when selected thresholds are crossed and export electrocardiogram reports.

Key considerations
Frontier X2 is a wellness and fitness product, not a medical device. Its recordings and strain estimates cannot diagnose a heart condition or confirm that exercise is safe. Accurate data requires firm skin contact, and advanced insights are offered through an optional subscription.