During any stage of your app's lifecycle, the onTrimMemory() callback also tells you when the overall device memory is getting low. You should respond by further releasing resources based on the following memory levels delivered by onTrimMemory(), This gist allows you to log the different states.

OnTrimMemoryActivity.java

@Override
public void onTrimMemory(int level) {
    Map<Integer, String> constantMap = getConstantMap();
    switch (level) {
        case TRIM_MEMORY_RUNNING_MODERATE:
            Log.e(TAG, getConstantName(constantMap, TRIM_MEMORY_RUNNING_MODERATE));
            break;
        case TRIM_MEMORY_RUNNING_LOW:
            Log.e(TAG, getConstantName(constantMap, TRIM_MEMORY_RUNNING_LOW));
            break;
        case TRIM_MEMORY_RUNNING_CRITICAL:
            Log.e(TAG, getConstantName(constantMap, TRIM_MEMORY_RUNNING_CRITICAL));
            break;
        case TRIM_MEMORY_UI_HIDDEN:
            Log.e(TAG, getConstantName(constantMap, TRIM_MEMORY_UI_HIDDEN));
            break;
        case TRIM_MEMORY_BACKGROUND:
            Log.e(TAG, getConstantName(constantMap, TRIM_MEMORY_BACKGROUND));
            break;
        case TRIM_MEMORY_MODERATE:
            Log.e(TAG, getConstantName(constantMap, TRIM_MEMORY_MODERATE));
            break;
        case TRIM_MEMORY_COMPLETE:
            Log.e(TAG, getConstantName(constantMap, TRIM_MEMORY_COMPLETE));
            break;
        default:
            Log.e(TAG, "Default Case Hit!");
            break;
    }
}

private static Map<Integer, String> getConstantMap() {
    Map<Integer, String> constantMap = new HashMap<>();
    for (Field field : ComponentCallbacks2.class.getDeclaredFields()) {
        if (((field.getModifiers() & (Modifier.FINAL | Modifier.STATIC)) != 0) && int.class == field.getType()) {
            // only record final static int fields
            try {
                constantMap.put(field.getInt(null), field.getName());
            } catch (IllegalAccessException e) {
                Log.e(TAG, e.getMessage());
            }
        }
    }
    return constantMap;
}