Privacy-First Flutter Apps Keep Sensitive Data On the Device

A developer describes HerCycle, a period tracker that stores cycle logs, symptom history, and health reports only on the phone. The app requires no account or server sync, works fully offline, and includes a PIN and biometric lock. The article argues that privacy should be an architectural decision made from the start rather than a settings option. It sets out core rules, such as keeping data local by default and sending nothing without explicit user action. It also compares local storage tools like SharedPreferences, sqflite, and flutter_secure_storage for different kinds of data.