Android: How to change the ActionBar "Home" Icon to be something other than the app icon?

The ActionBar will use the android:logo attribute of your manifest, if one is provided. That lets you use separate drawable resources for the icon (Launcher) and the logo (ActionBar, among other things).

In AndroidManifest.xml:

<application
    android:icon="@drawable/launcher"
    android:label="@string/app_name"
    android:name="com..."
    android:theme="@style/Theme">...</Application>

In styles.xml: (See android:icon)

<style name="Theme" parent="@android:style/Theme.Holo.Light">
    <item name="android:actionBarStyle">@style/ActionBar</item>
</style>
<style name="ActionBar" parent="@android:style/Widget.Holo.Light.ActionBar">
    <item name="android:icon">@drawable/icon</item>
</style>

Please try this line

getSupportActionBar().setHomeAsUpIndicator(R.drawable.back_arrow);

If you are using AppCompat, the only way to set the ActionBar icon on devices running Gingerbread (API 10) or below is by setting the android:icon attribute in every Activity in your manifest or setting the drawable programatically.

<manifest>
    <application>
        ...
        <activity android:name="com.your.ActivityName"
            ...
            android:icon="@drawable/ab_logo"/>
        ...
   </application>
</manifest>

Update: Be warned however that the application icon will be overridden if you set the android:icon attribute on the launch Activity. The only work around I know of is to have a splash or dummy Activity which then launches your main Activity.