Privacy

Last updated: 28 August 2026

4-6 has no account, no sign-up and no server. The short reason: the app does not need any of that to work, and what is never collected cannot be lost.

What stays on your device

Your sessions, the recorded beat intervals, the figures computed from them and your settings are stored only on your iPhone. They are not transmitted, not analysed and not backed up anywhere except by your own iPhone backup.

Apple Health

If you allow it, 4-6 reads your date of birth and sex from Apple Health so reference ranges can be matched to your age, and writes back mindful minutes. SDNN is only written if you switch it on, and it is off by default: paced breathing lifts that figure well above your resting value, and writing it would shift the baseline other apps read from the same place. All of it is optional, revocable at any time in the iOS settings, and the app works without it. This data does not leave your device.

Bluetooth

Bluetooth is used for one thing: connecting to a heart rate chest strap. There is no location tracking and no logging of devices around you.

Purchase and subscription

The subscription is sold entirely by Apple. We never see your name, your payment details or your Apple ID. The app only asks Apple whether an entitlement exists.

No tracking

There are no analytics SDKs, no third-party crash reporting, no ad networks and no advertising identifiers. How you use the app is not measured.

This website

foursix.app runs on our own servers in Germany. No analytics cookies are set. A single technical cookie remembers your language if you switch it, and is deleted when you close the browser. The site is served through Cloudflare, which processes the connection data technically required to do so.

Your rights

Because we hold no personal data about you, there is nothing for us to disclose or delete. You remove all of the app's data by deleting the app. Questions are welcome at [email protected].

Contact

Privacy questions go to [email protected].