diff --git a/gpsrelaysentinel/src/main/java/cc/winboll/studio/gpsrelaysentinel/MainService.java b/gpsrelaysentinel/src/main/java/cc/winboll/studio/gpsrelaysentinel/MainService.java
index 1bad227..976a6db 100644
--- a/gpsrelaysentinel/src/main/java/cc/winboll/studio/gpsrelaysentinel/MainService.java
+++ b/gpsrelaysentinel/src/main/java/cc/winboll/studio/gpsrelaysentinel/MainService.java
@@ -15,21 +15,26 @@ public class MainService extends Service {
     public static final String TAG = "MainService";
     private LocationManager mLocationManager;
     private LocationListener mLocationListener;
+    private boolean mIsRunning = false;
 
     @Override
     public void onCreate() {
         super.onCreate();
         LogUtils.d(TAG, "Service onCreate");
-        initLocation();
     }
 
     @Override
     public int onStartCommand(Intent intent, int flags, int startId) {
         LogUtils.d(TAG, "Service onStartCommand");
+        run();
         return START_STICKY;
     }
 
-    private void initLocation() {
+    private void run() {
+        if (mIsRunning) {
+            LogUtils.d(TAG, "GPS updates already running");
+            return;
+        }
         mLocationManager = (LocationManager) getSystemService(Context.LOCATION_SERVICE);
         mLocationListener = new LocationListener() {
             @Override
@@ -62,6 +67,7 @@ public class MainService extends Service {
                     mLocationListener
                 );
                 LogUtils.d(TAG, "GPS location updates requested");
+                mIsRunning = true;
             }
         } catch (SecurityException e) {
             LogUtils.e(TAG, "Permission denied: " + e.getMessage());
@@ -83,6 +89,7 @@ public class MainService extends Service {
                 LogUtils.e(TAG, "Permission denied when removing updates: " + e.getMessage());
             }
         }
+        mIsRunning = false;
         LogUtils.d(TAG, "Service onDestroy");
     }
 }