What is FLUX?
FLUX is an iOS running app that syncs your music's BPM to your live heart rate in real time, based on your personal physiological profile. Instead of a static playlist, the right track from your own library plays automatically, matched to your effort.
Do I need a watch or heart-rate sensor?
Not necessarily — FLUX works both ways, and you choose. With a heart-rate sensor (Apple Watch or Bluetooth), FLUX syncs to your live heart rate and your personal training zones. Without one, it syncs to your cadence — your phone counts your steps per minute and matches the music's BPM to your stride. Same real-time sync, no extra gear. Have a sensor but still want to run by cadence? That works too.
Which watches and sensors work with FLUX?
Apple Watch (via Apple Health), and Bluetooth heart-rate devices including chest straps (Polar, Wahoo, COROS, Garmin HRM), plus Garmin, Polar, COROS and WHOOP watches in "broadcast heart rate" mode. Chest straps are the most reliable. Fitbit and Samsung Galaxy Watch don't broadcast to third-party apps.
Do I need Apple Music?
Yes — FLUX plays from your own Apple Music library, so an active Apple Music subscription is required.
Is my data private — especially my heart rate?
Yes. Health data from Apple Health is used only to power app features. We never use it for advertising and never sell it. See our
Privacy Policy for details.
What is a Sync Score?
A score for how closely your body stayed in sync with the music during your run. It turns an abstract metric into something you can chase — and share.
How much does it cost?
Pricing is being finalized. FLUX will offer a free tier with premium features available via subscription. Join the updates list to hear first.
When will FLUX be on the App Store?
FLUX is live in TestFlight and heading to the App Store soon.
Sign up for updates to know the moment it launches.