https://www.vice.com/en_us/article/y3pgvg/the-1-period-tracker-on-the-app-store-will-hand-over-data-without-a-warrant

Stardust, an astrology-focused menstrual tracking app that launched on the App Store last year, is one of Apple’s top three most-downloaded free apps right now. From sometime around Sunday evening until Monday mid-morning, it was in the number one spot. It’s also one of very few apps that has put in writing that it will voluntarily—without even being legally required to—comply with law enforcement if it’s asked to share user data. 

After the fall of Roe on Friday, ending the Constitutional right to an abortion and making abortion illegal in more than a dozen states, many people used Twitter to urge others to delete their period tracking apps for privacy and security reasons. A widely-shared concern is that law enforcement can use personal data created in apps against people who’ve sought or gotten abortions illegally.