We just launched Clio Daye, a free Period tracker / menstrual cycle tracking app for iOS. No accounts. No ads. No server. Fully open source.
That last part is the point. Privacy in health apps is usually a policy promise. We wanted it to be a structural guarantee.
What We Found Before We Shipped
Before launching, we wanted to understand what we were up against. So we scraped the App Store and analyzed 289 menstrual cycle tracking apps currently available on iOS.
What we found was not subtle. https://pjaol.github.io/safeflow/period-tracker-privacy.html
Of the top 18 apps we examined in depth, 15 share data with third parties, 15 contain advertising-related language in their privacy policy, and all 18 require an account or cloud sync. Three had explicit data-selling language. Nearly every app (96.5%) is listed as free to download. Most of them are free the way social media is free: you pay with your data.
The biggest players have the longest paper trails.
Flo, the market leader with 1.83 million App Store reviews, settled a class action in 2025 for $59.5 million after sharing reproductive health data with Meta, Google, and others via in-app SDKs, without user consent.
Premom settled with the FTC after secretly sharing data with third parties despite its privacy policy saying otherwise.
Stardust surged to the top of the App Store after Dobbs by marketing itself as end-to-end encrypted, then was found uploading its own encryption keys to their server.
Ovia sold employer dashboards that showed HR departments which employees had high-risk pregnancies and when new mothers planned to return to work.
This is not a case of a few bad actors. It is a structural feature of how the market works. When user data is the business model, users are the product.
Why We Built It The Way We Did
We could not find a period tracker that was genuinely on-device and open source enough to prove it. So we built one.
Clio Daye stores everything in iOS local storage and the iOS Keychain. There are no network calls. There is no server. There is no backend to breach, no company acquisition that changes the data use terms, no warrant that reaches your data because your data never leaves your phone.
The source code is public on GitHub for anyone to verify and keep us honest. You can check that there are no third-party SDKs, no network calls, and that data never leaves the device. Privacy as a verifiable fact rather than a marketing claim is the entire premise.
What Clio Daye Actually Does
The app is built for people who want a practical, honest tracker, not a wellness platform with a subscription funnel.
You can log period, flow, symptoms, and mood in a few seconds. Cycle predictions are based on your actual history rather than an assumed 28-day average that may not fit you at all. Patterns emerge over time with links to trusted health resources rather than product upsells. The whole thing is protected by Face ID, Touch ID, or PIN, and you can delete everything in one tap.
It is free. There is no premium tier. There is no ad-supported version. There is nothing to upgrade to because this is the whole thing.
The Broader Moment This Comes From
We are writing this in April 2026. The legal and political landscape around reproductive health data has changed substantially in recent years. Data brokers operate with minimal restriction in most US states. Period tracking data has been identified as a potential source of evidence in states where abortion is criminalized. A privacy policy is not protection against a subpoena. It is not protection against a data breach. It is not protection against an acquisition that changes the terms of service two years from now.
On-device storage is. There is nothing to subpoena if there is no server. There is nothing to breach. There is no company policy to change.
Of the 289 apps we analyzed, we found three that showed signals of true on-device operation with no account required. None of them are open source, which means their privacy claims rest entirely on trust. Clio Daye is the only one we know of that is both on-device and open source.
What You Should Ask About Your Current App
If you use a period tracking app, read its privacy policy with these specific questions in mind.
Does it require an account? If so, your data lives on a server you do not control. Does it mention sharing with partners or advertising? That is usually where the money comes from. Is it open source? If not, its privacy claims are unverifiable. Where is the company registered? US companies operate under inconsistent state-level protections. EU companies face GDPR. Companies in some jurisdictions face minimal accountability at all.
If you want an app where none of those questions apply, try Clio Daye.
Download Clio Daye · Source code · Full research findings
We also wrote about this on LinkedIn if you want to share it there.