# ADR 0002: Android system time update capability

## Question

Can NTP Check update the Android device system time?

## Finding

For a normal Play/user-installed Android app: **no**. Android protects system clock changes behind privileged APIs/permissions. An app can measure offset and show guidance, but it cannot directly set wall-clock time unless it is installed with elevated trust.

## Practical options

1. **Normal app behavior for v1**
   - Probe NTP servers.
   - Show estimated device offset.
   - Warn when local clock appears wrong.
   - Provide a button to open Android Date & Time settings.
   - No special permissions beyond `INTERNET`.

2. **Device-owner / enterprise-managed device**
   - Some Android management APIs allow a device owner/profile owner to control certain time/timezone policies depending on Android version and ownership mode.
   - This requires provisioning the app as a device policy controller, not a typical install.

3. **Privileged/system app or custom ROM**
   - A system-signed or `/system/priv-app` application can use privileged permissions such as `android.permission.SET_TIME`.
   - This is not available to ordinary APK installs.

4. **Rooted device helper**
   - A rooted-device mode could call shell commands such as `date`/`toybox date`, but this is out of scope for v1 and has safety/security risks.

## Decision

V1 will not set Android system time. It will remain a diagnostic/comparison tool and may include an "Open Date & Time settings" action. Any future clock-setting mode must be explicitly separate and gated as enterprise/device-owner, privileged-system, or rooted-device functionality.

## Product implication

Market the app as an NTP testing and comparison dashboard, not as a general Android time synchronization daemon.