diff --git a/Service/AlarmService.cs b/Service/AlarmService.cs
index 00d36e8..b624c21 100644
--- a/Service/AlarmService.cs
+++ b/Service/AlarmService.cs
@@ -56,7 +56,13 @@ namespace LY.App.Service
                 entity = entity.Where(s => checkDistance(s.drone_lat, s.drone_lon, deviceinfo.Lat, deviceinfo.Lon) == true).ToList();
                 if (O4entity.Any())
                 {
-                    entity.AddRange(O4entity);
+                    foreach (var item in O4entity)
+                    {
+                        if (!entity.Exists(s => s.serial_number == item.serial_number))
+                        {
+                            entity.Add(item);
+                        }
+                    }
                 }
                 if (entity.Any())
                 {