Derny — Privacy Policy

Last updated: October 14, 2026

Derny (“the app”, “we”) is an indoor training app that connects to a Bluetooth smart trainer or treadmill and heart-rate monitor and drives adaptive workouts based on your live metrics. This policy explains what data the app handles and why.

The short version: The app works fully without an account, but while Derny is in beta the rides you record, how you use the app, and diagnostics about the machines you connect are shared with us to improve the app even if you never create one — see “Beta data sharing” below. If you sign in, your account email is stored too, and your workouts and ride history sync across your devices. You can delete your account and data from inside the app at any time; the rides you recorded are then kept without your name, email or account. The app has no ads or advertising trackers. The website counts visits without cookies, and uses limited conversion measurement for our Reddit ads.

Beta data sharing

While Derny is in beta, the app signs your device in automatically with a random, anonymous identifier the first time you open it. The rides you record — their metrics, the warm-up measurements the app uses to model your fitness, usage events, and diagnostics about the machines you connect (both described below) — are uploaded to our cloud under that identifier. This happens with no account, and during the beta it is not optional: it is how we find bugs and confirm that adaptive workouts behave correctly on real trainers and treadmills. The identifier is not your name, your email, or any advertising identifier, and we do not use this data for advertising. It is pseudonymous rather than anonymous: it links your rides, usage events and diagnostics to each other, and to your account if you create one. If you later create an account, that same identifier becomes your account, so the rides you already recorded stay yours. Deleting a ride in the app marks it deleted on our servers and removes its recorded samples; the remaining summary record is erased when the account or install it belongs to is deleted. You can delete everything this identifier holds from inside the app, with or without an account — see “Your choices and data deletion” below. An anonymous identifier carries no email address, so we have no way to match an emailed request to an install that never signed in: for those installs, deletion is in the app only.

Information we handle

• Account information. If you choose to create an account or sign in (with Apple, Google, or email), we store your email address to identify your account. Signing in is optional.
• Workouts and ride data. The workouts you create and the rides you record, including metrics such as power, cadence, heart rate, duration, and timestamps. This is stored on your device and synced to our cloud: during the beta from every install, and outside the beta only when you are signed in.
• Bluetooth device data. The app reads live data from your smart trainer or treadmill and heart-rate monitor over Bluetooth to display metrics and adjust workout targets. Your ride metrics are processed on your device and leave it as part of a ride you save, and, rarely, inside a private machine diagnostic recording (see below).
• Usage events. The app records how it is used: which screens it showed and whether they loaded, which buttons and messages were available or shown, what you tapped, and whether it worked, how long it took and how many times it was retried. For example, it records that the Start button was shown but disabled because no machine was connected, or that a save failed and was retried. Events are fixed codes chosen by us. They never contain text you typed, workout names, email addresses, web links or health readings, and they are not screen recordings. Each event carries the app version and build, your phone’s operating system version (such as iOS 18 or Android 14, never the exact release), whether it is a phone or a tablet, and broad screen-size and text-size settings. A few older ride events record a ride’s length, the machine’s model and, when you release the heart-rate safety hold, your heart rate at that moment. The app keeps events on your phone until they can be uploaded, so events recorded offline arrive later.
• Machine connection details. Each time you connect a smart trainer, treadmill or elliptical, including attempts that fail, we record technical information about that machine and that attempt: the model family its name matches (never the name itself, which you may have changed), the manufacturer, model and firmware details the machine reports about itself, the control features it reports (such as ERG/power-target and resistance support on a trainer, or speed control on a treadmill) and their supported ranges, and how each step went, from connecting and taking control through starting, saving and syncing a workout. The app never reads the machine’s serial number and never sends extra commands to the machine to collect any of this. It contains no health readings.
• Private machine diagnostics. When a machine does something unexpected, such as sending data the app can’t read, refusing a command or dropping the connection, the app may keep a short recording from around that moment: up to a minute before and twenty seconds after. It holds the technical messages the machine sent and received and what the app decided in response. Where a decision used your heart rate or power, the recording includes those readings, and we treat it as private health and fitness data. The app also occasionally keeps one recording from a machine that worked normally. Recordings are capped in size, and each install and account sends at most a few a day. Only we can read them.
• Crash reports and performance diagnostics. Every install sends crash reports and performance diagnostics — hangs, excessive CPU or disk use, and whether a session ended in a crash — to Sentry, our error-reporting provider. These describe what the app was doing when it failed: no name, no email address, no account or anonymous identifier, and no ride or workout content. They are sent from every install, with or without an account, and there is no setting in the app to switch them off.
• Apple Health and Health Connect (optional). With your permission, the app saves your finished rides to Apple Health on iPhone or Health Connect on Android: a smart-trainer ride as an indoor cycling workout, and a treadmill ride as an indoor walking or running workout. Treadmill rides do not include power or cadence, since treadmills do not report those. To estimate your maximum heart rate during onboarding, the app may read your resting heart rate — and, on iPhone, your date of birth — from Apple Health or Health Connect; it reads nothing else, including your past workouts. Health data is managed by Apple or Google on your device.
• Beta signup email. If you ask for a beta invite on our website, we store the email address you enter so we can send you your TestFlight invite and occasional beta updates, and so you can reply to us. We record whether you opened or clicked that email to gauge interest. You can unsubscribe at any time via the link in the email, and we will delete your address on request. We do not sell it or use it for advertising. We also store how you reached the form: any campaign tags in the link you followed, and the address of the page that linked to us, without its query string. That tells us which of our own posts and ads actually bring riders in. To carry it across our own pages, your browser holds it in session storage, which belongs to one tab and is gone when you close it. We receive none of it unless you submit the form.
• Reddit ad measurement. The beta signup page uses the Reddit Pixel. It records a page visit and, only after our signup endpoint accepts the form, a signup event. We do not give Reddit your email address, platform choice, form contents, account data, or ride data. Reddit receives the browser request and its own identifiers so it can attribute those two events to our ads. The pixel is not part of the app.
• Website visit counting. Our website pages use Cloudflare Web Analytics so we can see how many people reach them. It records the address of the page you opened, the address of the page that linked you to it, basic timings for how quickly the page loaded, and, from the request your browser makes, your country, your browser, your operating system, and whether you are on a phone, tablet, or desktop. It sets no cookies, reads nothing from your browser storage, and does not fingerprint your device, so it cannot recognize you from one visit to the next or follow you to other sites. It is not part of the app.

The app does not collect your location, contacts, photos, or advertising identifiers, and contains no advertising or cross-app tracking SDKs. It does not record your screen. We use Sentry for crash reporting, as described above, and keep our own usage events and machine diagnostics in our own backend, never in Sentry.

How long we keep it

Machine connection details, the detailed usage events about screens, buttons and outcomes, and private machine diagnostic recordings are deleted 30 days after we receive them. We keep summaries per machine model, such as how often a model connected successfully, for up to 12 months; they contain no identifier and nothing about you. Older, simpler usage events (such as app opened or ride started) are kept for up to 12 months. Your rides and account data are kept until you delete them, as described below.

How we use it

Data is used solely to provide and improve the app’s features: to store and sync your workouts and ride history, show your training metrics, (optionally) mirror finished rides to Apple Health or Health Connect, and keep the app working reliably across different smart trainers and treadmills. We use the website events described above only to measure our own Reddit ads, and the visit counts only to see how many people reach our pages and how many of them go on to sign up. We do not use your email, account data, or ride data for advertising.

Where your data is stored

When you are signed in, your account and ride data are stored using Supabase, our cloud backend provider, which processes this data on our behalf. During the beta your rides are stored there whether or not you have an account; outside the beta, when you are signed out your data stays only on your device. Our website is served by Cloudflare, which also provides the cookieless visit counting described above and processes it on our behalf. The crash reports and performance diagnostics described above are processed on our behalf by Sentry, in their United States data region.

Sharing

We do not sell your personal data. We share account and ride data only with the service providers above, strictly to operate the app, and where required by law. We share the limited website events described above with Reddit to measure our ads, but not your email address or app data.

Your choices and data deletion

You can use the app without an account, though during the beta your rides are still shared with us as described above. You can delete your data at any time from inside the app, on iPhone or Android, under Settings → About → Delete account (or Delete my data if you never signed in). If you can no longer use the app, email us at the address below from the address you signed in with, or tell us the email on your account, and we will delete the account within a reasonable period; an install that never signed in can only be deleted from inside the app, because we have no way to match an emailed request to it. Step-by-step instructions are on our account deletion page.

When you delete, we delete your account and email address, your name, your profile (such as date of birth, weight, heart-rate values and FTP), your Strava connection (we revoke Derny’s access with Strava first), any access you granted to AI assistants or other connected apps, the workouts you created, and the usage events, machine connection details and private machine diagnostic recordings linked to you. The app also erases everything it stored on that device, including usage events and diagnostics still waiting to upload, and returns to guest mode. Signing out also discards anything still waiting to upload, so it can never be attached to the next account that signs in. Machine model summaries, which contain nothing about you, are not affected.

What we keep. The rides you recorded are kept, without your identity, as ride data we use only to improve Derny: the power, heart-rate, cadence, speed and treadmill-belt measurements, the structure of the workout, the kind of machine, and the results of adaptive workouts. Before a ride is kept we remove what would tie it to you or to your other rides: it carries no account or install identifier and no replacement identifier that would join your rides together, no names of your devices, nothing you typed (such as workout names or notes), no Strava ids, only the date of the ride rather than its start time, and your profile (age, weight, FTP, heart-rate settings and max auto speed) only as broad ranges. The ride’s own recorded measurements, and the targets and adjustments Derny made during it, are kept as recorded, so they can still hint approximately at some profile values. After that we have no way to connect a kept ride back to your account, so we cannot find or remove it on request afterwards. The measurements themselves are kept as recorded, so a ride you also shared publicly elsewhere, such as on Strava, could in principle be matched by someone comparing the two. Kept rides may be moved into our anonymous ride store some time after your account is deleted rather than immediately. Rides you deleted in the app before deleting your account are not kept.

Deletion does not reach copies held elsewhere. After deletion, a copy of your rides and profile may remain in your own phone backup (iCloud or device backup on iPhone, Google backup on Android) and could be restored onto a reinstalled app or a new phone. Derny does not control those backups; delete them there if you want them gone. A restored copy is not sent back to us while you stay signed out, but if you sign in again, or if the restored app was never signed in and starts a new anonymous beta session, restored rides may be uploaded again. Likewise, rides already uploaded to Strava stay on Strava, and workouts saved to Apple Health or Health Connect are controlled by you in those apps. A beta invite email given on our website is kept separately and deleted on request.

Security

Data in transit is protected with standard encryption (HTTPS/TLS), and cloud data is protected by access controls so each account can only reach its own records.

Children

Derny is not directed to children under 13, and we do not knowingly collect personal information from them.

Changes

We may update this policy as the app evolves. Material changes will be reflected here with a new “last updated” date.

Contact

Questions or requests: leo@derny.app.