diff --git a/YD_AllHeartRates.Api/Mqtt/MqttBackgroundService.cs b/YD_AllHeartRates.Api/Mqtt/MqttBackgroundService.cs
index 6ccbcc8..c8233b2 100644
--- a/YD_AllHeartRates.Api/Mqtt/MqttBackgroundService.cs
+++ b/YD_AllHeartRates.Api/Mqtt/MqttBackgroundService.cs
@@ -89,8 +89,11 @@ namespace YD_AllHeartRates.Api.Mqtt
                 List<StudentDto> studentList;
                 List<S_Device> devices;
 
-                studentList = _caching.Get<List<StudentDto>>(AppSettings.StudentListCacheKey);
-                devices = _caching.Get<List<S_Device>>(AppSettings.DeviceListCacheKey);
+                var studentListCacheKey = $"{AppSettings.StudentListCacheKey}_{AppSettings.SchoolCode}";
+                var deviceListCacheKey = $"{AppSettings.DeviceListCacheKey}_{AppSettings.SchoolCode}";
+
+                studentList = _caching.Get<List<StudentDto>>(studentListCacheKey);
+                devices = _caching.Get<List<S_Device>>(deviceListCacheKey);
 
                 if (studentList == null || devices == null)
                 {
@@ -114,10 +117,10 @@ namespace YD_AllHeartRates.Api.Mqtt
                                        DeviceType = d.DeviceType,
                                    }).ToList();
 
-                    devices = _smartSportsContext.Device.Where(x => x.SchoolCode == AppSettings.SchoolCode).ToList();
+                    devices = _smartSportsContext.Device.Where(x => x.SchoolCode == AppSettings.SchoolCode && !string.IsNullOrWhiteSpace(x.StudentNo)).ToList();
 
-                    _caching.AddObject(AppSettings.StudentListCacheKey, studentList, 28800);
-                    _caching.AddObject(AppSettings.DeviceListCacheKey, devices, 28800);
+                    _caching.AddObject(studentListCacheKey, studentList, 28800);
+                    _caching.AddObject(deviceListCacheKey, devices, 28800);
                 }
 
                 var heartRateEntities = new ConcurrentBag<HeartRateData>();
diff --git a/YD_AllHeartRates.Api/Utilities/AppSettings.cs b/YD_AllHeartRates.Api/Utilities/AppSettings.cs
index bf6ef4a..6677d0f 100644
--- a/YD_AllHeartRates.Api/Utilities/AppSettings.cs
+++ b/YD_AllHeartRates.Api/Utilities/AppSettings.cs
@@ -14,8 +14,9 @@
         public static string[] CorsUrls { get; set; }
         public static MqttConfig Mqtt { get; set; }
 
-        public static string StudentListCacheKey = $"student_list_{SchoolCode}";
-        public static string DeviceListCacheKey = $"device_list_{SchoolCode}";
+        public static string StudentListCacheKey = $"student_list";
+
+        public static string DeviceListCacheKey = $"device_list";
         public static string SchoolCode { get; set; }
 
         public static void Init(IConfiguration configuration)