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Get the app.
Kata runs on iPhone, with its own app for Apple Watch, on Android and in your browser. One account carries across all of them.
iPhone and Apple Watch
Kata is in the App Store: search for "Kata" on your iPhone and install it. The Apple Watch app comes with it. If your watch installs apps on its own, Kata appears there by itself; otherwise open the Watch app on your iPhone and install Kata from there. What the watch does is on Watch and widgets.
Android
Kata is in Google Play, for Android 8.0 and newer: search for "Kata" and install it. What it does, and what stays iPhone-only, is on Kata on Android.
On your computer
The web app needs nothing installed: open app.yourkata.com in a browser and sign in with your account.
Notifications
Allow notifications when Kata asks and it can nudge you at the right moments: water reminders, supplement slots, the evening review. You control what pings you, how it is delivered and your quiet hours in Settings, under Notifications, also reachable from your Profile. On Android, see Notifications on Android.
Your data lives per device. Moving to a new phone? A backup carries it across: see Backup and restore.