Range Freely: ECG Recorder. Last updated 28 October 2026. General questions are on the Support page.
DFA α1 is used in exercise physiology, mainly to look for the aerobic threshold. In this app it appears after the first moments of a session, and it is shown in grey, labelled Settling, until it has had time to steady. It works under exercise conditions, once you are warmed up. Readings taken at rest are not valid for threshold purposes. The full explanation is in About DFA α1, and how to run a steady-state test is there too.
The α1 the app calculates agrees closely with Kubios HRV Scientific from 47 to 190 beats per minute. Kubios is the software family used in the research behind the 0.75 figure. That tells you the calculation matches, not what the number means for you: how α1 relates to your own threshold varies between people.
Empty: the app is still collecting its first data, or too few recent beats are usable, so it holds the value back instead of showing something confident and wrong. Grey: the number is real but still settling. If it stays empty, check the strap fit. The status words are explained on the DFA α1 page.
α1 depends on choices an app makes about how it handles the signal and the display, so apps that treat beats or smoothing differently can read differently, sometimes by a lot at lower heart rates. To check ours, export a Kubios CSV from Review and run the same stretch in Kubios.
It records the single-lead ECG and every beat-to-beat interval to your phone and lets you review, zoom and mark them. It does not interpret the ECG and does not look for heart conditions.
A chest strap; we recommend the Polar H10, which is the one we have validated and the one that streams the ECG. A strap that reports only beat-to-beat (R-R) intervals should give DFA α1 and HRV but no ECG trace. The Apple Watch is optional: the watch app starts, stops and marks a session and shows heart rate, zone and the α1 readout. The iPhone app is complete without it.
No. The session is written to disk continuously, the app reconnects on its own, and the gap is recorded as a gap.
In Review, use the share button: a review PDF, or a Kubios-ready CSV, raw or cleaned. Export needs a subscription; viewing your first recording does not.
DFA α1, always. One saved recording and a small number of HRV readings are free to try. A yearly subscription unlocks unlimited recordings, HRV and export.
Settings > Subscription > Restore Purchases, or manage it in your Apple Account settings. Refunds go through Apple.