diff --git a/README.md b/README.md
index 7fc6550..ef2cb60 100644
--- a/README.md
+++ b/README.md
@@ -13,6 +13,7 @@ A lightweight web interface for meshcore-cli, providing browser-based access to
 - 💬 **View messages** - Display chat history with intelligent auto-refresh
 - 🔔 **Smart notifications** - Bell icon with unread message counter across all channels
 - 📊 **Per-channel badges** - Unread count displayed on each channel in selector
+- 🔄 **Cross-device sync** - Unread message status syncs across all devices (server-side storage)
 - ✉️ **Send messages** - Publish to any channel (140 byte limit for LoRa)
 - 💌 **Direct messages (DM)** - Send and receive private messages with delivery status tracking
 - 📡 **Channel management** - Create, join, and switch between encrypted channels
diff --git a/app/read_status.py b/app/read_status.py
new file mode 100644
index 0000000..756995b
--- /dev/null
+++ b/app/read_status.py
@@ -0,0 +1,198 @@
+"""
+Read Status Manager - Server-side storage for message read status
+
+Manages the last seen timestamps for channels and DM conversations,
+providing cross-device synchronization for unread message tracking.
+"""
+
+import json
+import logging
+import os
+from pathlib import Path
+from threading import Lock
+from app.config import config
+
+logger = logging.getLogger(__name__)
+
+# Thread-safe lock for file operations
+_status_lock = Lock()
+
+# Path to read status file
+READ_STATUS_FILE = Path(config.MC_CONFIG_DIR) / '.read_status.json'
+
+
+def _get_default_status():
+    """Get default read status structure"""
+    return {
+        'channels': {},  # {"0": timestamp, "1": timestamp, ...}
+        'dm': {}         # {"name_User1": timestamp, "pk_abc123": timestamp, ...}
+    }
+
+
+def load_read_status():
+    """
+    Load read status from disk.
+
+    Returns:
+        dict: Read status with 'channels' and 'dm' keys
+    """
+    with _status_lock:
+        try:
+            if not READ_STATUS_FILE.exists():
+                logger.info("Read status file does not exist, creating default")
+                return _get_default_status()
+
+            with open(READ_STATUS_FILE, 'r', encoding='utf-8') as f:
+                status = json.load(f)
+
+            # Validate structure
+            if not isinstance(status, dict):
+                logger.warning("Invalid read status structure, resetting")
+                return _get_default_status()
+
+            # Ensure both keys exist
+            if 'channels' not in status:
+                status['channels'] = {}
+            if 'dm' not in status:
+                status['dm'] = {}
+
+            logger.debug(f"Loaded read status: {len(status['channels'])} channels, {len(status['dm'])} DM conversations")
+            return status
+
+        except json.JSONDecodeError as e:
+            logger.error(f"Failed to parse read status file: {e}")
+            return _get_default_status()
+        except Exception as e:
+            logger.error(f"Error loading read status: {e}")
+            return _get_default_status()
+
+
+def save_read_status(status):
+    """
+    Save read status to disk.
+
+    Args:
+        status (dict): Read status with 'channels' and 'dm' keys
+
+    Returns:
+        bool: True if successful, False otherwise
+    """
+    with _status_lock:
+        try:
+            # Ensure directory exists
+            READ_STATUS_FILE.parent.mkdir(parents=True, exist_ok=True)
+
+            # Write atomically (write to temp file, then rename)
+            temp_file = READ_STATUS_FILE.with_suffix('.tmp')
+            with open(temp_file, 'w', encoding='utf-8') as f:
+                json.dump(status, f, indent=2)
+
+            # Atomic rename
+            temp_file.replace(READ_STATUS_FILE)
+
+            logger.debug(f"Saved read status: {len(status['channels'])} channels, {len(status['dm'])} DM conversations")
+            return True
+
+        except Exception as e:
+            logger.error(f"Error saving read status: {e}")
+            return False
+
+
+def mark_channel_read(channel_idx, timestamp):
+    """
+    Mark a channel as read up to a specific timestamp.
+
+    Args:
+        channel_idx (int or str): Channel index (will be converted to string)
+        timestamp (int or float): Unix timestamp of last read message
+
+    Returns:
+        bool: True if successful, False otherwise
+    """
+    try:
+        # Load current status
+        status = load_read_status()
+
+        # Update channel timestamp (ensure key is string for JSON compatibility)
+        channel_key = str(channel_idx)
+        status['channels'][channel_key] = int(timestamp)
+
+        # Save updated status
+        success = save_read_status(status)
+
+        if success:
+            logger.debug(f"Marked channel {channel_idx} as read at timestamp {timestamp}")
+
+        return success
+
+    except Exception as e:
+        logger.error(f"Error marking channel {channel_idx} as read: {e}")
+        return False
+
+
+def mark_dm_read(conversation_id, timestamp):
+    """
+    Mark a DM conversation as read up to a specific timestamp.
+
+    Args:
+        conversation_id (str): Conversation identifier (e.g., "name_User1" or "pk_abc123")
+        timestamp (int or float): Unix timestamp of last read message
+
+    Returns:
+        bool: True if successful, False otherwise
+    """
+    try:
+        # Load current status
+        status = load_read_status()
+
+        # Update DM timestamp
+        status['dm'][conversation_id] = int(timestamp)
+
+        # Save updated status
+        success = save_read_status(status)
+
+        if success:
+            logger.debug(f"Marked DM conversation {conversation_id} as read at timestamp {timestamp}")
+
+        return success
+
+    except Exception as e:
+        logger.error(f"Error marking DM conversation {conversation_id} as read: {e}")
+        return False
+
+
+def get_channel_last_seen(channel_idx):
+    """
+    Get last seen timestamp for a specific channel.
+
+    Args:
+        channel_idx (int or str): Channel index
+
+    Returns:
+        int: Unix timestamp, or 0 if never seen
+    """
+    try:
+        status = load_read_status()
+        channel_key = str(channel_idx)
+        return status['channels'].get(channel_key, 0)
+    except Exception as e:
+        logger.error(f"Error getting last seen for channel {channel_idx}: {e}")
+        return 0
+
+
+def get_dm_last_seen(conversation_id):
+    """
+    Get last seen timestamp for a specific DM conversation.
+
+    Args:
+        conversation_id (str): Conversation identifier
+
+    Returns:
+        int: Unix timestamp, or 0 if never seen
+    """
+    try:
+        status = load_read_status()
+        return status['dm'].get(conversation_id, 0)
+    except Exception as e:
+        logger.error(f"Error getting last seen for DM {conversation_id}: {e}")
+        return 0
diff --git a/app/routes/api.py b/app/routes/api.py
index 5fb505e..236d2a2 100644
--- a/app/routes/api.py
+++ b/app/routes/api.py
@@ -1793,3 +1793,141 @@ def update_device_settings_api():
             'success': False,
             'error': str(e)
         }), 500
+
+
+# =============================================================================
+# Read Status (Server-side message read tracking)
+# =============================================================================
+
+@api_bp.route('/read_status', methods=['GET'])
+def get_read_status_api():
+    """
+    Get server-side read status for all channels and DM conversations.
+
+    This replaces localStorage-based tracking to enable cross-device synchronization.
+
+    Returns:
+        JSON with read status:
+        {
+            "success": true,
+            "channels": {
+                "0": 1735900000,
+                "1": 1735900100
+            },
+            "dm": {
+                "name_User1": 1735900200,
+                "pk_abc123": 1735900300
+            }
+        }
+    """
+    try:
+        from app import read_status
+
+        status = read_status.load_read_status()
+
+        return jsonify({
+            'success': True,
+            'channels': status['channels'],
+            'dm': status['dm']
+        }), 200
+
+    except Exception as e:
+        logger.error(f"Error getting read status: {e}")
+        return jsonify({
+            'success': False,
+            'error': str(e),
+            'channels': {},
+            'dm': {}
+        }), 500
+
+
+@api_bp.route('/read_status/mark_read', methods=['POST'])
+def mark_read_api():
+    """
+    Mark a channel or DM conversation as read.
+
+    JSON body (one of the following):
+        {"type": "channel", "channel_idx": 0, "timestamp": 1735900000}
+        {"type": "dm", "conversation_id": "name_User1", "timestamp": 1735900200}
+
+    Returns:
+        JSON with result:
+        {
+            "success": true,
+            "message": "Channel marked as read"
+        }
+    """
+    try:
+        from app import read_status
+
+        data = request.get_json()
+
+        if not data:
+            return jsonify({
+                'success': False,
+                'error': 'Missing JSON body'
+            }), 400
+
+        msg_type = data.get('type')
+        timestamp = data.get('timestamp')
+
+        if not msg_type or not timestamp:
+            return jsonify({
+                'success': False,
+                'error': 'Missing required fields: type and timestamp'
+            }), 400
+
+        if msg_type == 'channel':
+            channel_idx = data.get('channel_idx')
+            if channel_idx is None:
+                return jsonify({
+                    'success': False,
+                    'error': 'Missing required field: channel_idx'
+                }), 400
+
+            success = read_status.mark_channel_read(channel_idx, timestamp)
+
+            if success:
+                return jsonify({
+                    'success': True,
+                    'message': f'Channel {channel_idx} marked as read'
+                }), 200
+            else:
+                return jsonify({
+                    'success': False,
+                    'error': 'Failed to save read status'
+                }), 500
+
+        elif msg_type == 'dm':
+            conversation_id = data.get('conversation_id')
+            if not conversation_id:
+                return jsonify({
+                    'success': False,
+                    'error': 'Missing required field: conversation_id'
+                }), 400
+
+            success = read_status.mark_dm_read(conversation_id, timestamp)
+
+            if success:
+                return jsonify({
+                    'success': True,
+                    'message': f'DM conversation {conversation_id} marked as read'
+                }), 200
+            else:
+                return jsonify({
+                    'success': False,
+                    'error': 'Failed to save read status'
+                }), 500
+
+        else:
+            return jsonify({
+                'success': False,
+                'error': f'Invalid type: {msg_type}. Must be "channel" or "dm"'
+            }), 400
+
+    except Exception as e:
+        logger.error(f"Error marking as read: {e}")
+        return jsonify({
+            'success': False,
+            'error': str(e)
+        }), 500
diff --git a/app/static/js/app.js b/app/static/js/app.js
index 8c91afd..795bca6 100644
--- a/app/static/js/app.js
+++ b/app/static/js/app.js
@@ -20,9 +20,9 @@ let dmUnreadCounts = {};  // Track unread DM counts per conversation
 document.addEventListener('DOMContentLoaded', async function() {
     console.log('mc-webui initialized');
 
-    // Load last seen timestamps from localStorage
-    loadLastSeenTimestamps();
-    loadDmLastSeenTimestamps();
+    // Load last seen timestamps from server
+    await loadLastSeenTimestampsFromServer();
+    await loadDmLastSeenTimestampsFromServer();
 
     // Restore last selected channel from localStorage
     const savedChannel = localStorage.getItem('mc_active_channel');
@@ -707,39 +707,64 @@ function escapeHtml(text) {
 }
 
 /**
- * Load last seen timestamps from localStorage
+ * Load last seen timestamps from server
  */
-function loadLastSeenTimestamps() {
+async function loadLastSeenTimestampsFromServer() {
     try {
-        const saved = localStorage.getItem('mc_last_seen_timestamps');
-        if (saved) {
-            lastSeenTimestamps = JSON.parse(saved);
-            console.log('Loaded last seen timestamps:', lastSeenTimestamps);
+        const response = await fetch('/api/read_status');
+        const data = await response.json();
+
+        if (data.success && data.channels) {
+            // Convert string keys to integers for channel indices
+            lastSeenTimestamps = {};
+            for (const [key, value] of Object.entries(data.channels)) {
+                lastSeenTimestamps[parseInt(key)] = value;
+            }
+            console.log('Loaded channel read status from server:', lastSeenTimestamps);
+        } else {
+            console.warn('Failed to load read status from server, using empty state');
+            lastSeenTimestamps = {};
         }
     } catch (error) {
-        console.error('Error loading last seen timestamps:', error);
+        console.error('Error loading read status from server:', error);
         lastSeenTimestamps = {};
     }
 }
 
 /**
- * Save last seen timestamps to localStorage
+ * Save channel read status to server
  */
-function saveLastSeenTimestamps() {
+async function saveChannelReadStatus(channelIdx, timestamp) {
     try {
-        localStorage.setItem('mc_last_seen_timestamps', JSON.stringify(lastSeenTimestamps));
+        const response = await fetch('/api/read_status/mark_read', {
+            method: 'POST',
+            headers: {
+                'Content-Type': 'application/json'
+            },
+            body: JSON.stringify({
+                type: 'channel',
+                channel_idx: channelIdx,
+                timestamp: timestamp
+            })
+        });
+
+        const data = await response.json();
+
+        if (!data.success) {
+            console.error('Failed to save channel read status:', data.error);
+        }
     } catch (error) {
-        console.error('Error saving last seen timestamps:', error);
+        console.error('Error saving channel read status:', error);
     }
 }
 
 /**
  * Update last seen timestamp for current channel
  */
-function markChannelAsRead(channelIdx, timestamp) {
+async function markChannelAsRead(channelIdx, timestamp) {
     lastSeenTimestamps[channelIdx] = timestamp;
     unreadCounts[channelIdx] = 0;
-    saveLastSeenTimestamps();
+    await saveChannelReadStatus(channelIdx, timestamp);
     updateUnreadBadges();
 }
 
@@ -1172,29 +1197,50 @@ async function copyChannelKey() {
 // =============================================================================
 
 /**
- * Load DM last seen timestamps from localStorage
+ * Load DM last seen timestamps from server
  */
-function loadDmLastSeenTimestamps() {
+async function loadDmLastSeenTimestampsFromServer() {
     try {
-        const saved = localStorage.getItem('mc_dm_last_seen_timestamps');
-        if (saved) {
-            dmLastSeenTimestamps = JSON.parse(saved);
-            console.log('Loaded DM last seen timestamps:', Object.keys(dmLastSeenTimestamps).length);
+        const response = await fetch('/api/read_status');
+        const data = await response.json();
+
+        if (data.success && data.dm) {
+            dmLastSeenTimestamps = data.dm;
+            console.log('Loaded DM read status from server:', Object.keys(dmLastSeenTimestamps).length, 'conversations');
+        } else {
+            console.warn('Failed to load DM read status from server, using empty state');
+            dmLastSeenTimestamps = {};
         }
     } catch (error) {
-        console.error('Error loading DM last seen timestamps:', error);
+        console.error('Error loading DM read status from server:', error);
         dmLastSeenTimestamps = {};
     }
 }
 
 /**
- * Save DM last seen timestamps to localStorage
+ * Save DM read status to server
  */
-function saveDmLastSeenTimestamps() {
+async function saveDmReadStatus(conversationId, timestamp) {
     try {
-        localStorage.setItem('mc_dm_last_seen_timestamps', JSON.stringify(dmLastSeenTimestamps));
+        const response = await fetch('/api/read_status/mark_read', {
+            method: 'POST',
+            headers: {
+                'Content-Type': 'application/json'
+            },
+            body: JSON.stringify({
+                type: 'dm',
+                conversation_id: conversationId,
+                timestamp: timestamp
+            })
+        });
+
+        const data = await response.json();
+
+        if (!data.success) {
+            console.error('Failed to save DM read status:', data.error);
+        }
     } catch (error) {
-        console.error('Error saving DM last seen timestamps:', error);
+        console.error('Error saving DM read status:', error);
     }
 }
 
diff --git a/app/static/js/dm.js b/app/static/js/dm.js
index 2b43cfd..7497b65 100644
--- a/app/static/js/dm.js
+++ b/app/static/js/dm.js
@@ -24,8 +24,8 @@ document.addEventListener('DOMContentLoaded', async function() {
     // Force reflow to ensure proper layout calculation
     document.body.offsetHeight;
 
-    // Load last seen timestamps from localStorage
-    loadDmLastSeenTimestamps();
+    // Load last seen timestamps from server
+    await loadDmLastSeenTimestampsFromServer();
 
     // Setup event listeners
     setupEventListeners();
@@ -601,37 +601,59 @@ function setupEmojiPicker() {
 }
 
 /**
- * Load DM last seen timestamps from localStorage
+ * Load DM last seen timestamps from server
  */
-function loadDmLastSeenTimestamps() {
+async function loadDmLastSeenTimestampsFromServer() {
     try {
-        const saved = localStorage.getItem('mc_dm_last_seen_timestamps');
-        if (saved) {
-            dmLastSeenTimestamps = JSON.parse(saved);
+        const response = await fetch('/api/read_status');
+        const data = await response.json();
+
+        if (data.success && data.dm) {
+            dmLastSeenTimestamps = data.dm;
+            console.log('Loaded DM read status from server:', Object.keys(dmLastSeenTimestamps).length, 'conversations');
+        } else {
+            console.warn('Failed to load DM read status from server, using empty state');
+            dmLastSeenTimestamps = {};
         }
     } catch (error) {
-        console.error('Error loading last seen timestamps:', error);
+        console.error('Error loading DM read status from server:', error);
         dmLastSeenTimestamps = {};
     }
 }
 
 /**
- * Save DM last seen timestamps to localStorage
+ * Save DM read status to server
  */
-function saveDmLastSeenTimestamps() {
+async function saveDmReadStatus(conversationId, timestamp) {
     try {
-        localStorage.setItem('mc_dm_last_seen_timestamps', JSON.stringify(dmLastSeenTimestamps));
+        const response = await fetch('/api/read_status/mark_read', {
+            method: 'POST',
+            headers: {
+                'Content-Type': 'application/json'
+            },
+            body: JSON.stringify({
+                type: 'dm',
+                conversation_id: conversationId,
+                timestamp: timestamp
+            })
+        });
+
+        const data = await response.json();
+
+        if (!data.success) {
+            console.error('Failed to save DM read status:', data.error);
+        }
     } catch (error) {
-        console.error('Error saving last seen timestamps:', error);
+        console.error('Error saving DM read status:', error);
     }
 }
 
 /**
  * Mark conversation as read
  */
-function markAsRead(conversationId, timestamp) {
+async function markAsRead(conversationId, timestamp) {
     dmLastSeenTimestamps[conversationId] = timestamp;
-    saveDmLastSeenTimestamps();
+    await saveDmReadStatus(conversationId, timestamp);
 
     // Update dropdown to remove unread indicator
     populateConversationSelector();