Android – Wake Up and Unlock Device

I solved the issue. The reason we observed different behaviour when the device was plugged in via USB was because the device’s CPU was not going to sleep. I assume this is either a result of the debug mode setting, or simply how it behaves when plugged in to a computer since the power-saving feature of CPU-sleeping would be irrelevant. Obviously, when the device is not plugged in, the CPU would happily take a nap, and while we did observe the application randomly running (it would wake itself up at random times), the timing would be inconsistent. I further assume this is because the few CPU cycles that occurred are allocated sparingly, and our application would be given very few cycles at “random” times.

So our solution was to grab a partial wake lock when the device goes into the background (which is done in the onPause method), and release the lock in the onResume method. This seems to prevent the CPU from sleeping. We continue to use the full wake lock and keyguard disable to wake the device when we need to. Using the partial wake lock seems to keep the CPU from sleeping, and the device does appear to wake up properly when expected. Here is our updated code, in case anyone comes across this issue:

// Called from onCreate
protected void createWakeLocks(){
    PowerManager powerManager = (PowerManager) getSystemService(Context.POWER_SERVICE);
    fullWakeLock = powerManager.newWakeLock((PowerManager.SCREEN_BRIGHT_WAKE_LOCK | PowerManager.FULL_WAKE_LOCK | PowerManager.ACQUIRE_CAUSES_WAKEUP), "Loneworker - FULL WAKE LOCK");
    partialWakeLock = powerManager.newWakeLock(PowerManager.PARTIAL_WAKE_LOCK, "Loneworker - PARTIAL WAKE LOCK");
}

// Called implicitly when device is about to sleep or application is backgrounded
protected void onPause(){
    super.onPause();
    partialWakeLock.acquire();
}

// Called implicitly when device is about to wake up or foregrounded
protected void onResume(){
    super.onResume();
    if(fullWakeLock.isHeld()){
        fullWakeLock.release();
    }
    if(partialWakeLock.isHeld()){
        partialWakeLock.release();
    }
}

// Called whenever we need to wake up the device
public void wakeDevice() {
    fullWakeLock.acquire();

    KeyguardManager keyguardManager = (KeyguardManager) getSystemService(Context.KEYGUARD_SERVICE);
    KeyguardLock keyguardLock = keyguardManager.newKeyguardLock("TAG");
    keyguardLock.disableKeyguard();
}