diff --git a/CampusAppWP8/CampusAppWP8/Pages/Campusmap/CampusMapPage.xaml.cs b/CampusAppWP8/CampusAppWP8/Pages/Campusmap/CampusMapPage.xaml.cs
index 3c1b10b3..1cab6f8f 100644
--- a/CampusAppWP8/CampusAppWP8/Pages/Campusmap/CampusMapPage.xaml.cs
+++ b/CampusAppWP8/CampusAppWP8/Pages/Campusmap/CampusMapPage.xaml.cs
@@ -175,7 +175,10 @@ namespace CampusAppWP8.Pages.Campusmap
                 }
             }
 
-            this.ndefId = this.device.SubscribeForMessage(Constants.NCFMessageType_NDEF, this.NDEFHandler);
+            if (device != null)
+            {
+                this.ndefId = this.device.SubscribeForMessage(Constants.NCFMessageType_NDEF, this.NDEFHandler);
+            }
         }
 
         /// <summary> Methods overrides the  OnNavigatedFrom-Method. </summary>
@@ -183,7 +186,10 @@ namespace CampusAppWP8.Pages.Campusmap
         /// <seealso cref="M:System.Windows.Controls.Page.OnNavigatedFrom(NavigationEventArgs)"/>
         protected override void OnNavigatedFrom(NavigationEventArgs e)
         {
-            this.device.StopSubscribingForMessage(this.ndefId);
+            if (device != null)
+            {
+                this.device.StopSubscribingForMessage(this.ndefId);
+            }
 
             base.OnNavigatedFrom(e);
         }
@@ -489,6 +495,10 @@ namespace CampusAppWP8.Pages.Campusmap
         /// <param name="message"> the message of the device. </param>
         private void NDEFHandler(ProximityDevice sender, ProximityMessage message)
         {
+            if (device == null)
+            {
+                return;
+            }
             // create ndefMessage
             this.device.StopSubscribingForMessage(message.SubscriptionId);
             var ndefMessage = message.Data;
diff --git a/CampusAppWP8/CampusAppWP8/Pages/StartPage.xaml.cs b/CampusAppWP8/CampusAppWP8/Pages/StartPage.xaml.cs
index 9f84551d..e6daa710 100644
--- a/CampusAppWP8/CampusAppWP8/Pages/StartPage.xaml.cs
+++ b/CampusAppWP8/CampusAppWP8/Pages/StartPage.xaml.cs
@@ -119,7 +119,10 @@ namespace CampusAppWP8.Pages
         protected override void OnNavigatedTo(NavigationEventArgs e)
         {
             base.OnNavigatedTo(e);
-            this.ndefId = this.device.SubscribeForMessage(Constants.NCFMessageType_NDEF, this.NDEFHandler);
+            if (device != null)
+            {
+                this.ndefId = this.device.SubscribeForMessage(Constants.NCFMessageType_NDEF, this.NDEFHandler);
+            }
         }
 
         /// <summary> Methods overrides the  OnNavigatedFrom-Method. </summary>
@@ -127,7 +130,10 @@ namespace CampusAppWP8.Pages
         /// <seealso cref="M:System.Windows.Controls.Page.OnNavigatedFrom(NavigationEventArgs)"/>
         protected override void OnNavigatedFrom(NavigationEventArgs e)
         {
-            this.device.StopSubscribingForMessage(this.ndefId);
+            if (device != null)
+            {
+                this.device.StopSubscribingForMessage(this.ndefId);
+            }
 
             base.OnNavigatedFrom(e);
         }
@@ -378,6 +384,11 @@ namespace CampusAppWP8.Pages
         /// <param name="message"> The message. </param>
         private void NDEFHandler(ProximityDevice sender, ProximityMessage message)
         {
+            if (device == null)
+            {
+                return;
+            }
+
             // create ndefMessage
             this.device.StopSubscribingForMessage(message.SubscriptionId);
             var ndefMessage = message.Data;