diff --git a/app/build.gradle b/app/build.gradle
index 4b3a404..642a542 100644
--- a/app/build.gradle
+++ b/app/build.gradle
@@ -9,7 +9,7 @@ android {
         applicationId "ch.dissem.apps.abit"
         minSdkVersion 19
         targetSdkVersion 23
-        versionCode 3
+        versionCode 5
         versionName "1.0-beta"
     }
     signingConfigs {
@@ -29,16 +29,17 @@ android {
     }
 }
 
+ext.jabitVersion = '1.0.0'
 dependencies {
     compile fileTree(dir: 'libs', include: ['*.jar'])
     compile 'com.android.support:appcompat-v7:23.1.1'
     compile 'com.android.support:support-v4:23.1.1'
     compile 'com.android.support:design:23.1.1'
 
-    compile 'ch.dissem.jabit:jabit-core:0.2.1-SNAPSHOT'
-    compile 'ch.dissem.jabit:jabit-networking:0.2.1-SNAPSHOT'
-    compile 'ch.dissem.jabit:jabit-cryptography-spongy:0.2.1-SNAPSHOT'
-    compile 'ch.dissem.jabit:jabit-extensions:0.2.1-SNAPSHOT'
+    compile "ch.dissem.jabit:jabit-core:$jabitVersion"
+    compile "ch.dissem.jabit:jabit-networking:$jabitVersion"
+    compile "ch.dissem.jabit:jabit-cryptography-spongy:$jabitVersion"
+    compile "ch.dissem.jabit:jabit-extensions:$jabitVersion"
 
     compile 'org.slf4j:slf4j-android:1.7.12'
 
diff --git a/app/src/main/java/ch/dissem/apps/abit/notification/ProofOfWorkNotification.java b/app/src/main/java/ch/dissem/apps/abit/notification/ProofOfWorkNotification.java
index f677130..408bc5d 100644
--- a/app/src/main/java/ch/dissem/apps/abit/notification/ProofOfWorkNotification.java
+++ b/app/src/main/java/ch/dissem/apps/abit/notification/ProofOfWorkNotification.java
@@ -32,23 +32,30 @@ public class ProofOfWorkNotification extends AbstractNotification {
 
     public ProofOfWorkNotification(Context ctx) {
         super(ctx);
-        NotificationCompat.Builder builder = new NotificationCompat.Builder(ctx);
-
-        Intent showMessageIntent = new Intent(ctx, MainActivity.class);
-        PendingIntent pendingIntent = PendingIntent.getActivity(ctx, 0, showMessageIntent, PendingIntent.FLAG_UPDATE_CURRENT);
-
-        builder.setVisibility(NotificationCompat.VISIBILITY_PUBLIC)
-                .setUsesChronometer(true)
-                .setSmallIcon(R.drawable.ic_notification_proof_of_work)
-                .setContentTitle(ctx.getString(R.string.proof_of_work_title))
-                .setContentText(ctx.getString(R.string.proof_of_work_text))
-                .setContentIntent(pendingIntent);
-
-        notification = builder.build();
+        update(1);
     }
 
     @Override
     protected int getNotificationId() {
         return ONGOING_NOTIFICATION_ID;
     }
+
+    public ProofOfWorkNotification update(int numberOfItems) {
+        NotificationCompat.Builder builder = new NotificationCompat.Builder(ctx);
+
+        Intent showMessageIntent = new Intent(ctx, MainActivity.class);
+        PendingIntent pendingIntent = PendingIntent.getActivity(ctx, 0, showMessageIntent,
+                PendingIntent.FLAG_UPDATE_CURRENT);
+
+        builder.setVisibility(NotificationCompat.VISIBILITY_PUBLIC)
+                .setUsesChronometer(true)
+                .setOngoing(true)
+                .setSmallIcon(R.drawable.ic_notification_proof_of_work)
+                .setContentTitle(ctx.getString(R.string.proof_of_work_title))
+                .setContentText(ctx.getString(R.string.proof_of_work_text, numberOfItems))
+                .setContentIntent(pendingIntent);
+
+        notification = builder.build();
+        return this;
+    }
 }
diff --git a/app/src/main/java/ch/dissem/apps/abit/service/ProofOfWorkService.java b/app/src/main/java/ch/dissem/apps/abit/service/ProofOfWorkService.java
index 94b5620..7eee67d 100644
--- a/app/src/main/java/ch/dissem/apps/abit/service/ProofOfWorkService.java
+++ b/app/src/main/java/ch/dissem/apps/abit/service/ProofOfWorkService.java
@@ -22,10 +22,8 @@ import android.os.Binder;
 import android.os.IBinder;
 import android.support.annotation.Nullable;
 
-import org.slf4j.Logger;
-import org.slf4j.LoggerFactory;
-
-import java.lang.ref.WeakReference;
+import java.util.LinkedList;
+import java.util.Queue;
 
 import ch.dissem.apps.abit.notification.ProofOfWorkNotification;
 import ch.dissem.bitmessage.ports.MultiThreadedPOWEngine;
@@ -38,11 +36,12 @@ import static ch.dissem.apps.abit.notification.ProofOfWorkNotification.ONGOING_N
  * killed by the system before the nonce is found.
  */
 public class ProofOfWorkService extends Service {
-    public static final Logger LOG = LoggerFactory.getLogger(ProofOfWorkService.class);
-
     // Object to use as a thread-safe lock
     private static final Object lock = new Object();
     private static ProofOfWorkEngine engine;
+    private static boolean calculating;
+    private static final Queue<PowItem> queue = new LinkedList<>();
+    private static ProofOfWorkNotification notification;
 
     @Override
     public void onCreate() {
@@ -51,54 +50,74 @@ public class ProofOfWorkService extends Service {
                 engine = new MultiThreadedPOWEngine();
             }
         }
+        notification = new ProofOfWorkNotification(this);
     }
 
     @Nullable
     @Override
     public IBinder onBind(Intent intent) {
-        return new PowBinder(engine, this);
+        return new PowBinder(this);
     }
 
     public static class PowBinder extends Binder {
-        private final ProofOfWorkEngine engine;
+        private final ProofOfWorkService service;
 
-        private PowBinder(ProofOfWorkEngine engine, ProofOfWorkService service) {
-            this.engine = new EngineWrapper(engine, service);
+        private PowBinder(ProofOfWorkService service) {
+            this.service = service;
         }
 
-        public ProofOfWorkEngine getEngine() {
-            return engine;
+        public void process(PowItem item) {
+            synchronized (queue) {
+                service.startService(new Intent(service, ProofOfWorkService.class));
+                service.startForeground(ONGOING_NOTIFICATION_ID,
+                        notification.getNotification());
+                if (!calculating) {
+                    calculating = true;
+                    service.calculateNonce(item);
+                } else {
+                    queue.add(item);
+                    notification.update(queue.size()).show();
+                }
+            }
         }
     }
 
-    private static class EngineWrapper implements ProofOfWorkEngine {
-        private final ProofOfWorkNotification notification;
-        private final ProofOfWorkEngine engine;
-        private final WeakReference<ProofOfWorkService> serviceRef;
 
-        private EngineWrapper(ProofOfWorkEngine engine, ProofOfWorkService service) {
-            this.engine = engine;
-            this.serviceRef = new WeakReference<>(service);
-            this.notification = new ProofOfWorkNotification(service);
+    static class PowItem {
+        private final byte[] initialHash;
+        private final byte[] targetValue;
+        private final ProofOfWorkEngine.Callback callback;
+
+        PowItem(byte[] initialHash, byte[] targetValue, ProofOfWorkEngine.Callback callback) {
+            this.initialHash = initialHash;
+            this.targetValue = targetValue;
+            this.callback = callback;
         }
+    }
 
-        @Override
-        public void calculateNonce(byte[] initialHash, byte[] target, final Callback callback) {
-            final ProofOfWorkService service = serviceRef.get();
-            service.startService(new Intent(service, ProofOfWorkService.class));
-            service.startForeground(ONGOING_NOTIFICATION_ID, notification.getNotification());
-            engine.calculateNonce(initialHash, target, new ProofOfWorkEngine.Callback() {
-                @Override
-                public void onNonceCalculated(byte[] initialHash, byte[] nonce) {
-                    try {
-                        callback.onNonceCalculated(initialHash, nonce);
-                    } finally {
-                        service.stopForeground(true);
-                        service.stopSelf();
+    private void calculateNonce(final PowItem item) {
+        engine.calculateNonce(item.initialHash, item.targetValue, new ProofOfWorkEngine.Callback() {
+            @Override
+            public void onNonceCalculated(byte[] initialHash, byte[] nonce) {
+                try {
+                    item.callback.onNonceCalculated(initialHash, nonce);
+                } finally {
+                    PowItem item;
+                    synchronized (queue) {
+                        item = queue.poll();
+                        if (item == null) {
+                            calculating = false;
+                            stopForeground(true);
+                            stopSelf();
+                        } else {
+                            notification.update(queue.size()).show();
+                        }
+                    }
+                    if (item != null) {
+                        calculateNonce(item);
                     }
                 }
-            });
-
-        }
+            }
+        });
     }
 }
\ No newline at end of file
diff --git a/app/src/main/java/ch/dissem/apps/abit/service/ServicePowEngine.java b/app/src/main/java/ch/dissem/apps/abit/service/ServicePowEngine.java
index f986a7f..7211dcf 100644
--- a/app/src/main/java/ch/dissem/apps/abit/service/ServicePowEngine.java
+++ b/app/src/main/java/ch/dissem/apps/abit/service/ServicePowEngine.java
@@ -22,9 +22,11 @@ import android.content.Intent;
 import android.content.ServiceConnection;
 import android.os.IBinder;
 
-import java.util.concurrent.Semaphore;
+import java.util.LinkedList;
+import java.util.Queue;
 
 import ch.dissem.apps.abit.service.ProofOfWorkService.PowBinder;
+import ch.dissem.apps.abit.service.ProofOfWorkService.PowItem;
 import ch.dissem.bitmessage.ports.ProofOfWorkEngine;
 
 import static android.content.Context.BIND_AUTO_CREATE;
@@ -32,12 +34,12 @@ import static android.content.Context.BIND_AUTO_CREATE;
 /**
  * Proof of Work engine that uses the Proof of Work service.
  */
-public class ServicePowEngine implements ProofOfWorkEngine, ProofOfWorkEngine.Callback {
-    private final Semaphore semaphore = new Semaphore(1, true);
+public class ServicePowEngine implements ProofOfWorkEngine {
     private final Context ctx;
 
-    private byte[] initialHash, targetValue;
-    private Callback callback;
+    private static final Object lock = new Object();
+    private Queue<PowItem> queue = new LinkedList<>();
+    private PowBinder service;
 
     public ServicePowEngine(Context ctx) {
         this.ctx = ctx;
@@ -46,32 +48,31 @@ public class ServicePowEngine implements ProofOfWorkEngine, ProofOfWorkEngine.Ca
     private ServiceConnection connection = new ServiceConnection() {
         @Override
         public void onServiceConnected(ComponentName name, IBinder service) {
-            ((PowBinder) service).getEngine().calculateNonce(initialHash, targetValue, ServicePowEngine.this);
+            synchronized (lock) {
+                ServicePowEngine.this.service = (PowBinder) service;
+                while (!queue.isEmpty()) {
+                    ServicePowEngine.this.service.process(queue.poll());
+                }
+            }
         }
 
         @Override
         public void onServiceDisconnected(ComponentName name) {
-            semaphore.release();
+            service = null;
         }
     };
 
     @Override
     public void calculateNonce(byte[] initialHash, byte[] targetValue, Callback callback) {
-        try {
-            semaphore.acquire();
-        } catch (InterruptedException e) {
-            throw new RuntimeException(e);
+        PowItem item = new PowItem(initialHash, targetValue, callback);
+        synchronized (lock) {
+            if (service != null) {
+                service.process(item);
+            } else {
+                queue.add(item);
+                ctx.bindService(new Intent(ctx, ProofOfWorkService.class), connection,
+                        BIND_AUTO_CREATE);
+            }
         }
-        this.initialHash = initialHash;
-        this.targetValue = targetValue;
-        this.callback = callback;
-        ctx.bindService(new Intent(ctx, ProofOfWorkService.class), connection, BIND_AUTO_CREATE);
     }
-
-    @Override
-    public void onNonceCalculated(byte[] initialHash, byte[] bytes) {
-        callback.onNonceCalculated(initialHash, bytes);
-        ctx.unbindService(connection);
-    }
-
-}
+}
\ No newline at end of file
diff --git a/app/src/main/res/values-de/strings.xml b/app/src/main/res/values-de/strings.xml
index bc0d062..8a153f1 100644
--- a/app/src/main/res/values-de/strings.xml
+++ b/app/src/main/res/values-de/strings.xml
@@ -42,7 +42,7 @@
     <string name="connection_info_n">Stream %1$d: %2$d Verbindungen</string>
     <string name="connection_info_disconnected">Getrennt</string>
     <string name="connection_info_pending">Verbindung wird aufgebaut…</string>
-    <string name="proof_of_work_text">Warnung: dies könnte das Gerät erwärmen bis die Batterie leer ist.</string>
+    <string name="proof_of_work_text">Arbeite am Versenden (%1$d in Warteschlange)</string>
     <string name="proof_of_work_title">Proof of Work</string>
     <string name="error_invalid_sync_host">Synchronisation fehlgeschlagen: der vertrauenswürdige Knoten konnte nicht erreicht werden.</string>
     <string name="error_invalid_sync_port">Ungültiger Port in den Synchronisationseinstellungen: %s</string>
diff --git a/app/src/main/res/values/strings.xml b/app/src/main/res/values/strings.xml
index 7a4e21c..82daeff 100644
--- a/app/src/main/res/values/strings.xml
+++ b/app/src/main/res/values/strings.xml
@@ -44,7 +44,7 @@
     <string name="connection_info_disconnected">Disconnected</string>
     <string name="connection_info_pending">Connecting…</string>
     <string name="proof_of_work_title">Proof of Work</string>
-    <string name="proof_of_work_text">Warning: This might heat your device until the battery\'s dead.</string>
+    <string name="proof_of_work_text">Doing work to send message (%1$d queued)</string>
     <string name="error_invalid_sync_port">Invalid port in synchronization settings: %s</string>
     <string name="error_invalid_sync_host">Synchronization failed: Trusted node could not be reached.</string>
     <string name="compose_body_hint">Write message</string>