Thrumline

What it does

Thrumline connects to a Bluetooth heart rate strap and keeps the reading where you can see it: a heart that beats in time with your own, and the number beside it coloured by training zone. Click it and the session opens up.

• A dial marked with your own zones, so a glance tells you which band you are in.
• The recent line, coloured along its length by the zone each reading fell in.
• Time in zone, calories, heart rate variability and how far you have come down from the recent peak.
• A line about what your heart is actually doing, in plain words rather than numbers.
• Recorded sessions, when you want them: start a recording in the panel or under Settings ▸ Sessions, and look back at each one later with its graph, average, peak and time in zone.
• Export any recorded session as a CSV or TCX file.
• A zone alert while you record: a sound or a notification when your rate stays outside your target zone.

Requires macOS 14 Sonoma or later. Available in thirty-four languages.

Which sensors work

Any strap or armband that uses the standard Bluetooth Heart Rate Service, which is nearly all of them — chest straps and optical armbands alike. There is no allowlist and no per-device support: if it speaks the standard profile, it works.

Apple Watch is not supported. It does not broadcast the standard Bluetooth heart rate profile, and macOS has no way to read what it records. There is more about this, and about what does work, on the support page.

No sensor yet?

There is a worked example built in. Click See how it looks and the app runs on a four-minute session, so you can see exactly what it does before buying a strap. It is clearly labelled the whole time it runs, so a generated figure can never be mistaken for a reading.

Privacy in one paragraph

Thrumline has no network access at all, so your readings could not leave your Mac even if the app tried. There is no account, no analytics and no telemetry. Your zone settings and which sensor you last used are stored in the app's own sandbox container. The live readings are held in memory and are gone when the app quits; only the sessions you choose to record are kept, in the same container, and you can delete any of them in the app. Nothing leaves your Mac unless you export a session as a file yourself. The full privacy policy says the same thing at greater length.