 <p>You <em>might</em> be able to implement a <a href="http://developer.android.com/reference/android/app/admin/DeviceAdminReceiver.html#onPasswordFailed%28android.content.Context,%20android.content.Intent%29" rel="nofollow">DeviceAdminReceiver</a></p> <p>From it's description it should be notified of failed password attempts but it's not really clear from the description if that includes lock screen attempts.</p> <p>If that did work from a service or something you might be able to launch a toast though.</p> <hr> <p>[Edit] Found a better <a href="http://developer.android.com/guide/topics/admin/device-admin.html" rel="nofollow">resource</a></p>