diff --git a/ActivityMonitor.cs b/ActivityMonitor.cs
index 086e4de..3e5ebc5 100644
--- a/ActivityMonitor.cs
+++ b/ActivityMonitor.cs
@@ -10,17 +10,13 @@ namespace TimerApp
         Resting
     }
 
-    public class ActivityMonitor
+    public sealed class ActivityMonitor : IDisposable
     {
-        private System.Windows.Forms.Timer _timer;
-        private DateTime _lastWorkStartTime;
+        private readonly System.Windows.Forms.Timer _timer;
         private TimeSpan _accumulatedWorkTime;
-        private DateTime _restStartTime;
-        private int _restElapsedSeconds; // 休息已过秒数（用于避免时间计算导致的跳变）
-        private bool _isPaused = false; // 暂停状态
-        private DateTime _pauseStartTime; // 暂停开始时间
-        private TimeSpan _pauseDuration = TimeSpan.Zero; // 累计暂停时间（用于工作计时）
-        private int _restPauseStartSeconds = 0; // 休息暂停时的已过秒数
+        private int _restElapsedSeconds;
+        private bool _isPaused;
+        private bool _disposed;
 
         // 配置 (默认值)
         public TimeSpan WorkDuration { get; set; } = TimeSpan.FromMinutes(20);
@@ -31,11 +27,11 @@ namespace TimerApp
         public bool IsPaused { get; private set; } = false;
 
         // 事件
-        public event EventHandler<TimeSpan> WorkProgressChanged; // 剩余工作时间
-        public event EventHandler<TimeSpan> RestProgressChanged; // 剩余休息时间
-        public event EventHandler RestStarted;
-        public event EventHandler RestEnded;
-        public event EventHandler StateChanged;
+        public event EventHandler<TimeSpan>? WorkProgressChanged; // 剩余工作时间
+        public event EventHandler<TimeSpan>? RestProgressChanged; // 剩余休息时间
+        public event EventHandler? RestStarted;
+        public event EventHandler? RestEnded;
+        public event EventHandler? StateChanged;
 
         public ActivityMonitor()
         {
@@ -58,7 +54,6 @@ namespace TimerApp
         private void ResetWork()
         {
             _accumulatedWorkTime = TimeSpan.Zero;
-            _lastWorkStartTime = DateTime.Now;
             ChangeState(MonitorState.Idle);
         }
 
@@ -71,7 +66,7 @@ namespace TimerApp
             }
         }
 
-        private void Timer_Tick(object sender, EventArgs e)
+        private void Timer_Tick(object? sender, EventArgs e)
         {
             // 如果处于暂停状态，不处理计时逻辑
             if (_isPaused)
@@ -142,7 +137,6 @@ namespace TimerApp
                     {
                         // 从空闲变为工作
                         ChangeState(MonitorState.Working);
-                        _lastWorkStartTime = DateTime.Now;
                     }
 
                     // 累加工作时间
@@ -155,7 +149,6 @@ namespace TimerApp
                     if (remainingWork <= TimeSpan.Zero)
                     {
                         // 触发休息
-                        _restStartTime = DateTime.Now;
                         _restElapsedSeconds = 0; // 重置休息计数器
                         ChangeState(MonitorState.Resting);
                         RestStarted?.Invoke(this, EventArgs.Empty);
@@ -171,7 +164,6 @@ namespace TimerApp
         // 用于强制重置或测试
         public void ForceRest()
         {
-             _restStartTime = DateTime.Now;
              _restElapsedSeconds = 0; // 重置休息计数器
              ChangeState(MonitorState.Resting);
              RestStarted?.Invoke(this, EventArgs.Empty);
@@ -198,10 +190,8 @@ namespace TimerApp
         public void Restart()
         {
             _accumulatedWorkTime = TimeSpan.Zero;
-            _lastWorkStartTime = DateTime.Now;
             _isPaused = false;
             IsPaused = false;
-            _pauseDuration = TimeSpan.Zero;
 
             // Ensure timer is running
             if (!_timer.Enabled) _timer.Start();
@@ -219,13 +209,6 @@ namespace TimerApp
             {
                 _isPaused = true;
                 IsPaused = true;
-                _pauseStartTime = DateTime.Now;
-
-                // 如果正在休息，记录当前已过秒数
-                if (CurrentState == MonitorState.Resting)
-                {
-                    _restPauseStartSeconds = _restElapsedSeconds;
-                }
 
                 StateChanged?.Invoke(this, EventArgs.Empty);
             }
@@ -238,25 +221,19 @@ namespace TimerApp
                 _isPaused = false;
                 IsPaused = false;
 
-                // 计算暂停时长
-                TimeSpan pauseTime = DateTime.Now - _pauseStartTime;
-
-                // 如果正在工作，将暂停时间累加到暂停总时长中
-                // 这样工作时间就不会因为暂停而减少
-                if (CurrentState == MonitorState.Working)
-                {
-                    _pauseDuration += pauseTime;
-                }
-                // 如果正在休息，调整已过秒数，使剩余时间保持不变
-                else if (CurrentState == MonitorState.Resting)
-                {
-                    // 保持已过秒数不变，这样恢复后剩余时间不会变化
-                    // _restElapsedSeconds 保持不变
-                }
-
                 StateChanged?.Invoke(this, EventArgs.Empty);
                 RefreshStatus();
             }
         }
+
+        public void Dispose()
+        {
+            if (_disposed) return;
+            _disposed = true;
+
+            _timer.Stop();
+            _timer.Tick -= Timer_Tick;
+            _timer.Dispose();
+        }
     }
 }
diff --git a/AppSettings.cs b/AppSettings.cs
index cd3d5c4..29726bf 100644
--- a/AppSettings.cs
+++ b/AppSettings.cs
@@ -11,16 +11,26 @@ namespace TimerApp
         public int IdleThresholdSeconds { get; set; } = 30;
         public bool IsDarkMode { get; set; } = true;
 
-        private static string ConfigPath => Path.Combine(AppDomain.CurrentDomain.BaseDirectory, "settings.json");
+        private static string LegacyConfigPath => Path.Combine(AppDomain.CurrentDomain.BaseDirectory, "settings.json");
+
+        private static string ConfigPath
+        {
+            get
+            {
+                string dir = Path.Combine(Environment.GetFolderPath(Environment.SpecialFolder.LocalApplicationData), "TimerApp");
+                return Path.Combine(dir, "settings.json");
+            }
+        }
 
         public static AppSettings Load()
         {
             try
             {
-                if (File.Exists(ConfigPath))
+                string path = File.Exists(ConfigPath) ? ConfigPath : LegacyConfigPath;
+                if (File.Exists(path))
                 {
-                    string json = File.ReadAllText(ConfigPath);
-                    return JsonSerializer.Deserialize<AppSettings>(json);
+                    string json = File.ReadAllText(path);
+                    return JsonSerializer.Deserialize<AppSettings>(json) ?? new AppSettings();
                 }
             }
             catch
@@ -34,6 +44,7 @@ namespace TimerApp
         {
             try
             {
+                Directory.CreateDirectory(Path.GetDirectoryName(ConfigPath)!);
                 string json = JsonSerializer.Serialize(this, new JsonSerializerOptions { WriteIndented = true });
                 File.WriteAllText(ConfigPath, json);
             }
diff --git a/MainForm.Designer.cs b/MainForm.Designer.cs
index 772120a..01e2ee5 100644
--- a/MainForm.Designer.cs
+++ b/MainForm.Designer.cs
@@ -13,9 +13,11 @@ namespace TimerApp
         /// <param name="disposing">true if managed resources should be disposed; otherwise, false.</param>
         protected override void Dispose(bool disposing)
         {
-            if (disposing && (components != null))
+            if (disposing)
             {
-                components.Dispose();
+                _monitor?.Dispose();
+                _restForm?.Dispose();
+                components?.Dispose();
             }
             base.Dispose(disposing);
         }
diff --git a/MainForm.cs b/MainForm.cs
index dfca223..780f861 100644
--- a/MainForm.cs
+++ b/MainForm.cs
@@ -7,9 +7,9 @@ namespace TimerApp
 {
     public partial class MainForm : Form
     {
-        private ActivityMonitor _monitor;
+        private ActivityMonitor _monitor = null!;
         private AppSettings _settings;
-        private RestForm _restForm;
+        private RestForm? _restForm;
 
         // Colors
         private Color _darkBg = Color.FromArgb(30, 30, 30);
@@ -106,8 +106,8 @@ namespace TimerApp
             // Manual input validation
             txtWork.KeyPress += ValidateDigitInput;
             txtRest.KeyPress += ValidateDigitInput;
-            txtWork.Leave += (s, ev) => ValidateRange((TextBox)s, 1, 120);
-            txtRest.Leave += (s, ev) => ValidateRange((TextBox)s, 1, 30);
+            txtWork.Leave += (s, ev) => ValidateRange((TextBox)s!, 1, 120);
+            txtRest.Leave += (s, ev) => ValidateRange((TextBox)s!, 1, 30);
 
             // Focus handling (remove custom caret)
             txtWork.KeyDown += TextBox_KeyDown;
@@ -163,7 +163,7 @@ namespace TimerApp
             }
         }
 
-        private void ValidateDigitInput(object sender, KeyPressEventArgs e)
+        private void ValidateDigitInput(object? sender, KeyPressEventArgs e)
         {
             // Allow control keys (backspace, etc.) and digits
             if (!char.IsControl(e.KeyChar) && !char.IsDigit(e.KeyChar))
@@ -216,7 +216,7 @@ namespace TimerApp
 
         // CustomCaret removed to use system caret with centered text
 
-        private void TextBox_KeyDown(object sender, KeyEventArgs e)
+        private void TextBox_KeyDown(object? sender, KeyEventArgs e)
         {
             if (e.KeyCode == Keys.Enter)
             {
@@ -407,11 +407,11 @@ namespace TimerApp
             _monitor.IdleThreshold = TimeSpan.FromSeconds(_settings.IdleThresholdSeconds);
         }
 
-        private void Monitor_StateChanged(object sender, EventArgs e)
+        private void Monitor_StateChanged(object? sender, EventArgs e)
         {
             if (InvokeRequired)
             {
-                Invoke(new Action<object, EventArgs>(Monitor_StateChanged), sender, e);
+                Invoke(new Action<object?, EventArgs>(Monitor_StateChanged), sender, e);
                 return;
             }
             UpdateStatusUI();
@@ -456,11 +456,11 @@ namespace TimerApp
             }
         }
 
-        private void Monitor_WorkProgressChanged(object sender, TimeSpan remaining)
+        private void Monitor_WorkProgressChanged(object? sender, TimeSpan remaining)
         {
             if (InvokeRequired)
             {
-                Invoke(new Action<object, TimeSpan>(Monitor_WorkProgressChanged), sender, remaining);
+                Invoke(new Action<object?, TimeSpan>(Monitor_WorkProgressChanged), sender, remaining);
                 return;
             }
             lblTimeLeft.Text = $"{remaining.Minutes:D2}:{remaining.Seconds:D2}";
@@ -476,11 +476,11 @@ namespace TimerApp
             }
         }
 
-        private void Monitor_RestStarted(object sender, EventArgs e)
+        private void Monitor_RestStarted(object? sender, EventArgs e)
         {
             if (InvokeRequired)
             {
-                Invoke(new Action<object, EventArgs>(Monitor_RestStarted), sender, e);
+                Invoke(new Action<object?, EventArgs>(Monitor_RestStarted), sender, e);
                 return;
             }
 
@@ -494,13 +494,13 @@ namespace TimerApp
             _restForm.Show();
         }
 
-        private void RestForm_SkipRequested(object sender, EventArgs e)
+        private void RestForm_SkipRequested(object? sender, EventArgs e)
         {
             _monitor.Stop();
             _monitor.Start();
         }
 
-        private void Monitor_RestProgressChanged(object sender, TimeSpan remaining)
+        private void Monitor_RestProgressChanged(object? sender, TimeSpan remaining)
         {
             if (_restForm != null && !_restForm.IsDisposed && _restForm.Visible)
             {
@@ -508,11 +508,11 @@ namespace TimerApp
             }
         }
 
-        private void Monitor_RestEnded(object sender, EventArgs e)
+        private void Monitor_RestEnded(object? sender, EventArgs e)
         {
             if (InvokeRequired)
             {
-                Invoke(new Action<object, EventArgs>(Monitor_RestEnded), sender, e);
+                Invoke(new Action<object?, EventArgs>(Monitor_RestEnded), sender, e);
                 return;
             }
 
@@ -555,12 +555,12 @@ namespace TimerApp
             }
         }
 
-        private void notifyIcon1_MouseDoubleClick(object sender, MouseEventArgs e)
+        private void notifyIcon1_MouseDoubleClick(object? sender, MouseEventArgs e)
         {
             ShowForm();
         }
 
-        private void toolStripMenuItemShow_Click(object sender, EventArgs e)
+        private void toolStripMenuItemShow_Click(object? sender, EventArgs e)
         {
             ShowForm();
         }
diff --git a/NativeMethods.cs b/NativeMethods.cs
index b668bde..bc9637c 100644
--- a/NativeMethods.cs
+++ b/NativeMethods.cs
@@ -1,5 +1,7 @@
 using System;
 using System.Runtime.InteropServices;
+using System.Threading;
+using System.Threading.Tasks;
 using Windows.Media.Control;
 
 namespace TimerApp
@@ -26,22 +28,17 @@ namespace TimerApp
         /// <returns></returns>
         public static long GetIdleTime()
         {
-            LASTINPUTINFO lastInputInfo = new LASTINPUTINFO();
-            lastInputInfo.cbSize = (uint)Marshal.SizeOf(lastInputInfo);
-            lastInputInfo.dwTime = 0;
+            LASTINPUTINFO lastInputInfo = new LASTINPUTINFO
+            {
+                cbSize = (uint)Marshal.SizeOf<LASTINPUTINFO>(),
+                dwTime = 0
+            };
 
             if (GetLastInputInfo(ref lastInputInfo))
             {
-                // Environment.TickCount 可能会在大约 24.9 天后翻转为负数，
-                // 但 GetLastInputInfo 返回的也是 uint (DWORD)，所以我们统一转为 long 处理差值
-                // 或者直接使用 unchecked 减法处理溢出
-                // 更稳健的做法是使用 GetTickCount64 (Vista+)，但 Environment.TickCount 在 .NET Core 3.1+ 已经是 64位了(Environment.TickCount64)
-                // 这里为了兼容性，我们简单处理。注意 GetLastInputInfo 返回的是 uint 毫秒数。
-
-                long envTicks = Environment.TickCount;
-                // 处理 TickCount 翻转问题 (Environment.TickCount 是 int，GetLastInputInfo 是 uint)
-                // 简单的做法:
-                return (long)GetTickCount() - (long)lastInputInfo.dwTime;
+                uint tickCount = GetTickCount();
+                uint idleMs = unchecked(tickCount - lastInputInfo.dwTime);
+                return idleMs;
             }
 
             return 0;
@@ -56,27 +53,57 @@ namespace TimerApp
         /// <returns>如果有媒体正在播放返回 true，否则返回 false</returns>
         public static bool IsMediaPlaying()
         {
-            try
-            {
-                var sessionManager = GlobalSystemMediaTransportControlsSessionManager.RequestAsync().GetAwaiter().GetResult();
-                var sessions = sessionManager.GetSessions();
+            EnsureMediaPlaybackStatusFresh();
+            return Volatile.Read(ref _mediaPlaying);
+        }
 
-                foreach (var session in sessions)
+        private static bool _mediaPlaying;
+        private static long _mediaLastUpdateMs = -1;
+        private static int _mediaUpdateInProgress;
+
+        private static void EnsureMediaPlaybackStatusFresh()
+        {
+            long now = Environment.TickCount64;
+            long last = Interlocked.Read(ref _mediaLastUpdateMs);
+            if (last >= 0 && now - last < 3000)
+            {
+                return;
+            }
+
+            if (Interlocked.Exchange(ref _mediaUpdateInProgress, 1) == 1)
+            {
+                return;
+            }
+
+            _ = Task.Run(async () =>
+            {
+                bool playing = false;
+                try
                 {
-                    var playbackInfo = session.GetPlaybackInfo();
-                    if (playbackInfo.PlaybackStatus == GlobalSystemMediaTransportControlsSessionPlaybackStatus.Playing)
+                    var sessionManager = await GlobalSystemMediaTransportControlsSessionManager.RequestAsync();
+                    var sessions = sessionManager.GetSessions();
+
+                    foreach (var session in sessions)
                     {
-                        return true;
+                        var playbackInfo = session.GetPlaybackInfo();
+                        if (playbackInfo.PlaybackStatus == GlobalSystemMediaTransportControlsSessionPlaybackStatus.Playing)
+                        {
+                            playing = true;
+                            break;
+                        }
                     }
                 }
-            }
-            catch
-            {
-                // 如果 API 调用失败，返回 false（保守处理）
-                return false;
-            }
-
-            return false;
+                catch
+                {
+                    playing = false;
+                }
+                finally
+                {
+                    Volatile.Write(ref _mediaPlaying, playing);
+                    Interlocked.Exchange(ref _mediaLastUpdateMs, Environment.TickCount64);
+                    Interlocked.Exchange(ref _mediaUpdateInProgress, 0);
+                }
+            });
         }
     }
 }
diff --git a/RestForm.cs b/RestForm.cs
index 4f5a2ef..d54811a 100644
--- a/RestForm.cs
+++ b/RestForm.cs
@@ -6,11 +6,11 @@ namespace TimerApp
 {
     public class RestForm : Form
     {
-        private Label lblMessage;
-        private Label lblTimer;
-        private Button btnSkip;
+        private Label lblMessage = null!;
+        private Label lblTimer = null!;
+        private Button btnSkip = null!;
 
-        public event EventHandler SkipRequested;
+        public event EventHandler? SkipRequested;
 
         public RestForm()
         {
@@ -99,12 +99,12 @@ namespace TimerApp
             this.PerformLayout();
         }
 
-        private void RestForm_Load(object sender, EventArgs e)
+        private void RestForm_Load(object? sender, EventArgs e)
         {
             CenterControls();
         }
 
-        private void RestForm_Resize(object sender, EventArgs e)
+        private void RestForm_Resize(object? sender, EventArgs e)
         {
             CenterControls();
         }
@@ -153,7 +153,7 @@ namespace TimerApp
             }
         }
 
-        private void btnSkip_Click(object sender, EventArgs e)
+        private void btnSkip_Click(object? sender, EventArgs e)
         {
             SkipRequested?.Invoke(this, EventArgs.Empty);
             this.Close();
diff --git a/SingleInstanceManager.cs b/SingleInstanceManager.cs
index 21115d7..c1db749 100644
--- a/SingleInstanceManager.cs
+++ b/SingleInstanceManager.cs
@@ -11,12 +11,16 @@ namespace TimerApp
         private const string MutexName = "Local\\TimerApp.SingleInstance";
         private const string PipeName = "TimerApp.SingleInstancePipe";
 
-        private readonly Mutex _mutex;
+        private readonly Mutex? _mutex;
+        private readonly bool _ownsMutex;
+        private readonly bool _enableIpc;
         private readonly CancellationTokenSource _cts = new();
 
-        private SingleInstanceManager(Mutex mutex)
+        private SingleInstanceManager(Mutex? mutex, bool ownsMutex, bool enableIpc)
         {
             _mutex = mutex;
+            _ownsMutex = ownsMutex;
+            _enableIpc = enableIpc;
         }
 
         public static bool TryAcquire(out SingleInstanceManager? manager)
@@ -32,11 +36,12 @@ namespace TimerApp
                     return false;
                 }
 
-                manager = new SingleInstanceManager(mutex);
+                manager = new SingleInstanceManager(mutex, ownsMutex: true, enableIpc: true);
                 return true;
             }
             catch
             {
+                manager = new SingleInstanceManager(mutex: null, ownsMutex: false, enableIpc: false);
                 return true;
             }
         }
@@ -57,6 +62,7 @@ namespace TimerApp
 
         public void StartServer(Action onShowRequested)
         {
+            if (!_enableIpc) return;
             Task.Run(() => ServerLoop(onShowRequested, _cts.Token));
         }
 
@@ -104,15 +110,17 @@ namespace TimerApp
 
             try
             {
-                _mutex.ReleaseMutex();
+                if (_ownsMutex)
+                {
+                    _mutex?.ReleaseMutex();
+                }
             }
             catch
             {
             }
 
-            _mutex.Dispose();
+            _mutex?.Dispose();
             _cts.Dispose();
         }
     }
 }
-