Power Management

Battery life is a perennial user concern. To extend battery life, Android continually adds new features and optimizations to help the platform optimize the off-charger behavior of applications and devices.

Android includes the following battery life enhancements:

  • App Standby. The platform can place unused applications in App Standby mode, temporarily restricting network access and deferring syncs and jobs for those applications.
  • Doze. The platform can enter a state of deep sleep (periodically resuming normal operations) if users have not actively used their device (screen off and stationary) for extended periods of time. Android 7.0 also enables Doze to trigger a lighter set of optimizations when users turn off the device screen yet continue to move around.
  • Exemptions. System apps and cloud messaging services preloaded on a device are typically exempted from App Standby and Doze by default (although app developers can intent their applications into this setting). Users can exempt applications via the Settings menu.

The following sections describe these enhancements.

App Standby

App Standby extends battery life by deferring background network activity and jobs for applications the user is not actively using.

App Standby lifecycle

The platform detects inactive applications and places them in App Standby until the user begins actively engaging with the application.

Detection During App Standby Exit

The platform detects an application is inactive when the device is not charging and the user has not launched the application directly or indirectly for a specific amount of clock time as well as a specific amount of screen-on time. (Indirect launches occur when a foreground app accesses a service in a second app.)

The platform prevents applications from accessing the network more than once a day, deferring application syncs and other jobs.

The platform exits the app from App Standby when:

  • Application becomes active.
  • Device is plugged in and charging.

Active applications are unaffected by App Standby. An application is active when it has:

  • A process currently in the foreground (either as an activity or foreground service, or in use by another activity or foreground service), such as notification listener, accessibility services, live wallpaper, etc.
  • A notification viewed by the user, such as in the lock screen or notification tray.
  • Explicitly been launched by the user.

An application is inactive if none of the above activities has occurred for a period of time.

Testing App Standby

You can manually test App Standby using the following ADB commands:

$ adb shell dumpsys battery unplug
$ adb shell am set-idle packageName true
$ adb shell am set-idle packageName false
$ adb shell am get-idle packageName

Doze

Doze extends battery life by deferring application background CPU and network activity when a device is unused for long periods.

Idle devices in Doze periodically enter a maintenance window, during which apps can complete pending activities (syncs, jobs, etc.). Doze then resumes sleep for a longer period of time, followed by another maintenance window. The platform continues the Doze sleep/maintenance sequence, increasing the length of idle each time, until a maximum of a few hours of sleep time is reached. At all times, a device in Doze remains aware of motion and immediately leaves Doze if motion is detected.

Android 7.0 extends Doze to trigger a lighter set of optimizations every time a user turns off the device screen, even when the user continues to move around, enabling longer lasting battery life.

System services (such as telephony) may be preloaded and exempted from Doze by default. Users can also exempt specific applications from Doze in the Settings menu. By default, Doze is disabled in the Android Open Source Project (AOSP). For details on enabling Doze, see Integrating Doze.

Doze requirements

Doze support requires the device has a cloud messaging service, such as Google Cloud Messaging (GCM). This enables the device to know when to wake from Doze.

Full Doze support also requires a Significant Motion Detector (SMD) on the device; however, the lightweight Doze mode in Android 7.0 does not require an SMD. If Doze is enabled on a device that:

  • Has an SMD, full Doze optimizations occur (includes lightweight optimizations).
  • Does not have an SMD, only the lightweight Doze optimizations occur.

Doze lifecycle

Doze begins when the platform detects the device is idle and ends when one or more exit criteria activities occur.

Detection During Doze Exit

The platform detects a device is idle when:

  • Device is stationary (using significant motion detector).
  • Device screen is off for some amount of time.

Doze mode does not engage when the device is plugged into a power charger.

The platform attempts to keep the system in a sleep state, periodically resuming normal operations during a maintenance window then returning the device to sleep for longer repeating periods. During sleep, the following restrictions are active:

  • Apps not allowed network access.
  • App wakelocks ignored.
  • Alarms deferred. Excludes alarm clock alarms and alarms set using setAndAllowWhileIdle() (limited to 1 per 15 minutes per app while in Doze). This exemption is intended for apps (such as Calendar) that must show event reminder notifications.
  • Wi-Fi scans not performed.
  • SyncAdapter syncs and JobScheduler jobs deferred until the next maintenance window.
  • Apps receiving SMS and MMS messages are put on a temporary whitelist so they can complete their processing.

The platform exits the device from Doze when it detects:

  • User interaction with device.
  • Device movement.
  • Device screen turns on.
  • Imminent AlarmClock alarm.

Notifications do not cause the device to exit from Doze.

Android 7.0 extends Doze by enabling a lightweight sleep mode during screen off, before the device is idle.

Figure 1. Doze modes for non-stationary and stationary devices.

Action Doze Lightweight Doze
Trigger Screen off, on battery, stationary Screen off, on battery (unplugged)
Timing Successively increasing periods with maintenance Repeated N-minute periods with maintenance windows
Restrictions No network access, wake lock, or GPS/Wi-FI scan. Alarms and jobs/syncs deferred. No network access. Jobs/syncs deferred except during maintenance windows.
Behavior Only high-priority push notification messages received. All real-time messages (instant messages, calls, etc.) received. High-priority push notification message enables temporary network access.
Exit Motion, screen on, or alarm clock alarm. Screen on.

Interaction with App Standby

  • Time spent in Doze does not count towards App Standby.
  • While the device is in Doze, idle applications are allowed to perform normal operations at least once a day.

Integrating Doze

When Doze is enabled, devices that support SENSOR_TYPE_SIGNIFICANT_MOTION will perform full Doze optimizations (includes lightweight optimizations); devices without an SMD will perform only lightweight Doze optimizations. Android automatically selects the appropriate Doze optimizations and no vendor configuration is necessary.

To enable Doze for a device, perform the following tasks:

  1. Confirm the device has a cloud messaging service installed.
  2. In the device overlay config file overlay/frameworks/base/core/res/res/values/config.xml, set config_enableAutoPowerModes to true:
    bool name="config_enableAutoPowerModes">true</bool>
    

    In AOSP, this parameter is set to false (Doze disabled) by default.
  3. Confirm that preloaded apps and services:
  4. Confirm the necessary services are exempted from Doze.

Tips

Testing and optimizing applications

Test all applications (especially preloaded applications) in Doze mode. For details, refer to Testing Doze and App Standby.

Note: MMS/SMS/Telephony services function independently of Doze and will always wake client apps even while the device remains in Doze mode.

Exempting applications

You can exempt applications from being subject to Doze or App Standby. Exemptions may be needed in the following use cases:

  • OEM using non-GCM Cloud Messaging platform
  • Carrier using non-GCM Cloud Messaging platform
  • Third-party application using non-GCM Cloud Messaging platform

Warning: Do not exempt apps to avoid testing and optimizing. Unnecessary exemptions undermine the benefits of Doze and App Standby and can compromise the user experience, so we strongly suggest minimizing such exemptions as they allow applications to defeat beneficial controls the platform has over power use. If users become unhappy about the power consumption of these apps, it can lead to frustration, bad experiences (and negative user reviews for the app), and customer support questions. For these reasons, we strongly recommend that you do not exempt third-party applications and instead exempt only cloud messaging services or apps with similar functions.

Apps exempted by default are listed in a single view within the Settings > Battery menu. This list is used for exempting the app from both Doze and App Standby modes. To provide transparency to the user, the Settings menu MUST show all exempted applications.

Users can manually exempt apps via Settings > Battery > Battery optimization > All apps and then selecting the app to turn off (or back on) optimization. However, users cannot unexempt any application or service that is exempted by default in the system image.