diff --git a/static/css/adsb_dashboard.css b/static/css/adsb_dashboard.css
index e7c98b5..1af7360 100644
--- a/static/css/adsb_dashboard.css
+++ b/static/css/adsb_dashboard.css
@@ -418,6 +418,7 @@ body {
 }
 
 .aircraft-item {
+    position: relative;
     background: rgba(0, 0, 0, 0.3);
     border: 1px solid rgba(74, 158, 255, 0.15);
     border-radius: 4px;
diff --git a/templates/adsb_dashboard.html b/templates/adsb_dashboard.html
index 930054f..c7de9fd 100644
--- a/templates/adsb_dashboard.html
+++ b/templates/adsb_dashboard.html
@@ -100,7 +100,9 @@
                 <option value="military">Military</option>
                 <option value="civil">Civil</option>
                 <option value="emergency">Emergency</option>
+                <option value="watchlist">Watchlist</option>
             </select>
+            <button class="watchlist-btn" onclick="showWatchlistModal()" title="Manage Watchlist">★</button>
             <select id="rangeSelect" onchange="updateRange()" title="Range rings distance">
                 <option value="50">50nm</option>
                 <option value="100">100nm</option>
@@ -164,6 +166,9 @@
         let alertsEnabled = true;
         let currentView = 'map';  // 'map' or 'radar'
 
+        // Watchlist - persisted to localStorage
+        let watchlist = JSON.parse(localStorage.getItem('adsb_watchlist') || '[]');
+
         // Aircraft trails
         let aircraftTrails = {};  // ICAO -> [{lat, lon, alt, time}, ...]
         let trailLines = {};      // ICAO -> L.polyline (array of segments)
@@ -245,11 +250,16 @@
             if (alertedAircraft[icao]) return;
             const militaryInfo = isMilitaryAircraft(icao, ac.callsign);
             const squawkInfo = checkSquawkCode(ac);
+            const onWatchlist = isOnWatchlist(ac);
 
             if (squawkInfo) {
                 alertedAircraft[icao] = 'emergency';
                 playAlertSound('emergency');
                 showAlertBanner(`EMERGENCY: ${squawkInfo.name} - ${ac.callsign || icao}`, '#ff0000');
+            } else if (onWatchlist) {
+                alertedAircraft[icao] = 'watchlist';
+                playAlertSound('military');  // Use military sound for watchlist
+                showAlertBanner(`WATCHLIST: ${ac.callsign || ac.registration || icao} detected!`, '#00d4ff');
             } else if (militaryInfo.military) {
                 alertedAircraft[icao] = 'military';
                 playAlertSound('military');
@@ -278,6 +288,114 @@
             alertsEnabled = document.getElementById('alertToggle').checked;
         }
 
+        // ============================================
+        // WATCHLIST FUNCTIONS
+        // ============================================
+        function saveWatchlist() {
+            localStorage.setItem('adsb_watchlist', JSON.stringify(watchlist));
+        }
+
+        function isOnWatchlist(aircraft) {
+            const icao = aircraft.icao?.toUpperCase();
+            const callsign = aircraft.callsign?.toUpperCase()?.trim();
+            const registration = aircraft.registration?.toUpperCase()?.trim();
+
+            return watchlist.some(entry => {
+                const val = entry.value.toUpperCase();
+                if (entry.type === 'icao' && icao === val) return true;
+                if (entry.type === 'callsign' && callsign && callsign.includes(val)) return true;
+                if (entry.type === 'registration' && registration === val) return true;
+                if (entry.type === 'any') {
+                    if (icao === val) return true;
+                    if (callsign && callsign.includes(val)) return true;
+                    if (registration === val) return true;
+                }
+                return false;
+            });
+        }
+
+        function addToWatchlist(value, type = 'any', note = '') {
+            value = value.trim().toUpperCase();
+            if (!value) return false;
+
+            // Check for duplicates
+            const exists = watchlist.some(e => e.value.toUpperCase() === value && e.type === type);
+            if (exists) return false;
+
+            watchlist.push({ value, type, note, added: Date.now() });
+            saveWatchlist();
+            renderWatchlist();
+            return true;
+        }
+
+        function removeFromWatchlist(index) {
+            watchlist.splice(index, 1);
+            saveWatchlist();
+            renderWatchlist();
+        }
+
+        function showWatchlistModal() {
+            renderWatchlist();
+            document.getElementById('watchlistModal').classList.add('active');
+            document.getElementById('watchlistInput').focus();
+        }
+
+        function closeWatchlistModal() {
+            document.getElementById('watchlistModal').classList.remove('active');
+        }
+
+        function renderWatchlist() {
+            const container = document.getElementById('watchlistEntries');
+            document.getElementById('watchlistCount').textContent = watchlist.length;
+
+            if (watchlist.length === 0) {
+                container.innerHTML = '<div class="watchlist-empty">No entries. Add callsigns, registrations, or ICAO codes to watch.</div>';
+                return;
+            }
+
+            container.innerHTML = watchlist.map((entry, i) => `
+                <div class="watchlist-entry">
+                    <div class="watchlist-entry-info">
+                        <span class="watchlist-value">${entry.value}</span>
+                        <span class="watchlist-type">${entry.type}</span>
+                        ${entry.note ? `<span class="watchlist-note">${entry.note}</span>` : ''}
+                    </div>
+                    <button class="watchlist-remove" onclick="removeFromWatchlist(${i})" title="Remove">&times;</button>
+                </div>
+            `).join('');
+        }
+
+        // Close watchlist modal on overlay click or Escape key
+        document.getElementById('watchlistModal')?.addEventListener('click', (e) => {
+            if (e.target.id === 'watchlistModal') closeWatchlistModal();
+        });
+        document.addEventListener('keydown', (e) => {
+            if (e.key === 'Escape') {
+                closeWatchlistModal();
+                closeSquawkModal();
+            }
+        });
+
+        function handleWatchlistAdd() {
+            const input = document.getElementById('watchlistInput');
+            const type = document.getElementById('watchlistType').value;
+            const note = document.getElementById('watchlistNote').value.trim();
+
+            if (addToWatchlist(input.value, type, note)) {
+                input.value = '';
+                document.getElementById('watchlistNote').value = '';
+            }
+        }
+
+        function addCurrentAircraftToWatchlist() {
+            if (!selectedIcao || !aircraft[selectedIcao]) return;
+            const ac = aircraft[selectedIcao];
+            const value = ac.callsign || ac.registration || ac.icao;
+            const type = ac.callsign ? 'callsign' : (ac.registration ? 'registration' : 'icao');
+            addToWatchlist(value, type);
+            showAlertBanner(`Added ${value} to watchlist`, '#00d4ff');
+        }
+
         // ============================================
         // MILITARY/EMERGENCY DETECTION
         // ============================================
@@ -1020,6 +1138,7 @@
             if (currentFilter === 'military') return militaryInfo.military;
             if (currentFilter === 'civil') return !militaryInfo.military;
             if (currentFilter === 'emergency') return !!squawkInfo;
+            if (currentFilter === 'watchlist') return isOnWatchlist(ac);
             return true;
         }
 
@@ -1512,7 +1631,7 @@ sudo make install</code>
 
                 sortedAircraft.forEach(ac => {
                     const div = document.createElement('div');
-                    div.className = `aircraft-item ${selectedIcao === ac.icao ? 'selected' : ''}`;
+                    div.className = `aircraft-item ${selectedIcao === ac.icao ? 'selected' : ''} ${isOnWatchlist(ac) ? 'watched' : ''}`;
                     div.setAttribute('data-icao', ac.icao);
                     div.onclick = () => selectAircraft(ac.icao);
                     div.innerHTML = buildAircraftItemHTML(ac);
@@ -1531,7 +1650,7 @@ sudo make install</code>
                 sortedAircraft.forEach(ac => {
                     const existingItem = existingItems[ac.icao];
                     if (existingItem) {
-                        existingItem.className = `aircraft-item ${selectedIcao === ac.icao ? 'selected' : ''}`;
+                        existingItem.className = `aircraft-item ${selectedIcao === ac.icao ? 'selected' : ''} ${isOnWatchlist(ac) ? 'watched' : ''}`;
                         existingItem.innerHTML = buildAircraftItemHTML(ac);
                     }
                 });
@@ -2180,6 +2299,34 @@ sudo make install</code>
         </div>
     </div>
 
+    <!-- Watchlist Modal -->
+    <div id="watchlistModal" class="watchlist-modal">
+        <div class="watchlist-modal-content">
+            <div class="watchlist-modal-header">
+                <span>★ WATCHLIST</span>
+                <button class="watchlist-modal-close" onclick="closeWatchlistModal()">&times;</button>
+            </div>
+            <div class="watchlist-add-form">
+                <input type="text" id="watchlistInput" placeholder="Callsign, registration, or ICAO..." onkeypress="if(event.key==='Enter')handleWatchlistAdd()">
+                <select id="watchlistType">
+                    <option value="any">Any match</option>
+                    <option value="callsign">Callsign</option>
+                    <option value="registration">Registration</option>
+                    <option value="icao">ICAO Hex</option>
+                </select>
+                <input type="text" id="watchlistNote" placeholder="Note (optional)" style="flex:1;">
+                <button onclick="handleWatchlistAdd()">ADD</button>
+            </div>
+            <div class="watchlist-entries" id="watchlistEntries">
+                <div class="watchlist-empty">No entries. Add callsigns, registrations, or ICAO codes to watch.</div>
+            </div>
+            <div class="watchlist-footer">
+                <span class="watchlist-count"><span id="watchlistCount">0</span> entries</span>
+                <span class="watchlist-hint">Alerts trigger when watched aircraft appear</span>
+            </div>
+        </div>
+    </div>
+
     <style>
         .squawk-clickable {
             cursor: pointer;
@@ -2310,6 +2457,189 @@ sudo make install</code>
             padding: 4px;
             border-bottom: 1px solid var(--border-color, #444);
         }
+
+        /* Watchlist Button */
+        .watchlist-btn {
+            background: transparent;
+            border: 1px solid var(--border-color, #444);
+            color: var(--accent-cyan, #00d4ff);
+            padding: 4px 8px;
+            border-radius: 4px;
+            cursor: pointer;
+            font-size: 12px;
+            transition: all 0.2s;
+        }
+        .watchlist-btn:hover {
+            background: var(--accent-cyan, #00d4ff);
+            color: #000;
+        }
+
+        /* Watchlist Modal */
+        .watchlist-modal {
+            display: none;
+            position: fixed;
+            top: 0;
+            left: 0;
+            width: 100%;
+            height: 100%;
+            background: rgba(0, 0, 0, 0.8);
+            z-index: 1000;
+            justify-content: center;
+            align-items: center;
+        }
+        .watchlist-modal.active {
+            display: flex;
+        }
+        .watchlist-modal-content {
+            background: var(--bg-secondary, #1a1a1a);
+            border: 1px solid var(--border-color, #333);
+            border-radius: 8px;
+            width: 90%;
+            max-width: 500px;
+            max-height: 70vh;
+            overflow: hidden;
+            display: flex;
+            flex-direction: column;
+        }
+        .watchlist-modal-header {
+            display: flex;
+            justify-content: space-between;
+            align-items: center;
+            padding: 12px 16px;
+            background: var(--bg-tertiary, #252525);
+            border-bottom: 1px solid var(--border-color, #333);
+            font-weight: 600;
+            font-size: 12px;
+            letter-spacing: 0.1em;
+            color: var(--accent-cyan, #00d4ff);
+        }
+        .watchlist-modal-close {
+            background: none;
+            border: none;
+            color: var(--text-secondary, #888);
+            font-size: 20px;
+            cursor: pointer;
+        }
+        .watchlist-modal-close:hover {
+            color: #fff;
+        }
+        .watchlist-add-form {
+            display: flex;
+            gap: 8px;
+            padding: 12px;
+            background: var(--bg-tertiary, #252525);
+            border-bottom: 1px solid var(--border-color, #333);
+            flex-wrap: wrap;
+        }
+        .watchlist-add-form input,
+        .watchlist-add-form select {
+            padding: 6px 10px;
+            border: 1px solid var(--border-color, #444);
+            border-radius: 4px;
+            background: var(--bg-primary, #0d0d0d);
+            color: var(--text-primary, #fff);
+            font-size: 12px;
+        }
+        .watchlist-add-form input:first-child {
+            flex: 2;
+            min-width: 150px;
+        }
+        .watchlist-add-form button {
+            padding: 6px 16px;
+            background: var(--accent-cyan, #00d4ff);
+            color: #000;
+            border: none;
+            border-radius: 4px;
+            cursor: pointer;
+            font-weight: 600;
+            font-size: 11px;
+        }
+        .watchlist-add-form button:hover {
+            opacity: 0.9;
+        }
+        .watchlist-entries {
+            flex: 1;
+            overflow-y: auto;
+            padding: 8px;
+        }
+        .watchlist-empty {
+            text-align: center;
+            color: var(--text-secondary, #666);
+            padding: 30px;
+            font-size: 12px;
+        }
+        .watchlist-entry {
+            display: flex;
+            justify-content: space-between;
+            align-items: center;
+            padding: 10px 12px;
+            background: var(--bg-tertiary, #252525);
+            border-radius: 4px;
+            margin-bottom: 6px;
+        }
+        .watchlist-entry:hover {
+            background: var(--bg-primary, #1a1a1a);
+        }
+        .watchlist-entry-info {
+            display: flex;
+            align-items: center;
+            gap: 10px;
+            flex-wrap: wrap;
+        }
+        .watchlist-value {
+            font-family: 'JetBrains Mono', monospace;
+            font-weight: bold;
+            color: var(--accent-cyan, #00d4ff);
+            font-size: 13px;
+        }
+        .watchlist-type {
+            font-size: 9px;
+            padding: 2px 6px;
+            background: var(--bg-primary, #0d0d0d);
+            border-radius: 3px;
+            color: var(--text-secondary, #888);
+            text-transform: uppercase;
+        }
+        .watchlist-note {
+            font-size: 11px;
+            color: var(--text-secondary, #888);
+        }
+        .watchlist-remove {
+            background: none;
+            border: none;
+            color: var(--text-secondary, #666);
+            font-size: 18px;
+            cursor: pointer;
+            padding: 0 4px;
+        }
+        .watchlist-remove:hover {
+            color: #ff4444;
+        }
+        .watchlist-footer {
+            display: flex;
+            justify-content: space-between;
+            padding: 10px 16px;
+            background: var(--bg-tertiary, #252525);
+            border-top: 1px solid var(--border-color, #333);
+            font-size: 10px;
+            color: var(--text-secondary, #888);
+        }
+        .watchlist-hint {
+            opacity: 0.7;
+        }
+
+        /* Watched aircraft highlight in list */
+        .aircraft-item.watched {
+            border-left: 3px solid var(--accent-cyan, #00d4ff);
+        }
+        .aircraft-item.watched::before {
+            content: '★';
+            position: absolute;
+            right: 8px;
+            top: 8px;
+            color: var(--accent-cyan, #00d4ff);
+            font-size: 10px;
+        }
     </style>
 </body>
 </html>