diff --git a/muxplex/frontend/app.js b/muxplex/frontend/app.js
index 3892347..a8310e7 100644
--- a/muxplex/frontend/app.js
+++ b/muxplex/frontend/app.js
@@ -561,14 +561,35 @@ function renderSidebar(sessions, currentSession) {
     return;
   }
 
-  list.innerHTML = visible.map((session) => buildSidebarHTML(session, currentSession)).join('');
+  let html = '';
 
-  // Bind click handlers on each sidebar item
+  if (_sources.length > 1) {
+    // Group sessions by deviceName when multiple sources configured
+    const groups = new Map();
+    for (const session of visible) {
+      const deviceName = session.deviceName || 'Unknown';
+      if (!groups.has(deviceName)) groups.set(deviceName, []);
+      groups.get(deviceName).push(session);
+    }
+
+    for (const [deviceName, deviceSessions] of groups) {
+      html += `<h4 class="sidebar-device-header">${escapeHtml(deviceName)}</h4>`;
+      html += deviceSessions.map((session) => buildSidebarHTML(session, currentSession)).join('');
+    }
+  } else {
+    // Single source: flat list with no device headers
+    html = visible.map((session) => buildSidebarHTML(session, currentSession)).join('');
+  }
+
+  list.innerHTML = html;
+
+  // Bind click handlers on each sidebar item, passing sourceUrl
   if (typeof list.querySelectorAll === 'function') {
     list.querySelectorAll('.sidebar-item').forEach((item) => {
       const name = item.dataset.session;
+      const sourceUrl = item.dataset.sourceUrl || '';
       on(item, 'click', () => {
-        if (name !== currentSession) openSession(name);
+        if (name !== currentSession) openSession(name, { sourceUrl });
       });
     });
   }
diff --git a/muxplex/frontend/tests/test_app.mjs b/muxplex/frontend/tests/test_app.mjs
index 9c19d8f..9998e01 100644
--- a/muxplex/frontend/tests/test_app.mjs
+++ b/muxplex/frontend/tests/test_app.mjs
@@ -2666,4 +2666,75 @@ test('saveGridViewMode stores to localStorage when scope is local', () => {
   app._setGridViewMode('flat');
 });
 
+// --- renderSidebar device grouping (task-16) ---
+
+test('renderSidebar groups sessions by device with sidebar-device-header when multiple sources configured', () => {
+  let capturedHTML = '';
+  const mockList = {
+    get innerHTML() { return capturedHTML; },
+    set innerHTML(v) { capturedHTML = v; },
+    querySelectorAll: () => [],
+  };
+  const origGetById = globalThis.document.getElementById;
+  globalThis.document.getElementById = (id) => {
+    if (id === 'sidebar-list') return mockList;
+    return null;
+  };
+
+  // Set up multiple sources
+  app._setSources([
+    { url: '', name: 'Laptop', type: 'local', status: 'authenticated', backoffMs: 2000 },
+    { url: 'https://remote.example.com', name: 'Server', type: 'remote', status: 'authenticated', backoffMs: 2000 },
+  ]);
+
+  app._setViewMode('fullscreen');
+  const sessions = [
+    { name: 'alpha', deviceName: 'Laptop', sourceUrl: '', sessionKey: '::alpha', snapshot: '', bell: { unseen_count: 0 } },
+    { name: 'beta', deviceName: 'Server', sourceUrl: 'https://remote.example.com', sessionKey: 'https://remote.example.com::beta', snapshot: '', bell: { unseen_count: 0 } },
+  ];
+  app.renderSidebar(sessions, null);
+
+  assert.ok(capturedHTML.includes('sidebar-device-header'), 'sidebar HTML should contain sidebar-device-header elements when multiple sources');
+  assert.ok(capturedHTML.includes('Laptop'), 'sidebar HTML should contain device name "Laptop"');
+  assert.ok(capturedHTML.includes('Server'), 'sidebar HTML should contain device name "Server"');
+
+  // Cleanup
+  app._setSources([]);
+  globalThis.document.getElementById = origGetById;
+  app._setViewMode('grid');
+});
+
+test('renderSidebar does NOT group when only one source configured', () => {
+  let capturedHTML = '';
+  const mockList = {
+    get innerHTML() { return capturedHTML; },
+    set innerHTML(v) { capturedHTML = v; },
+    querySelectorAll: () => [],
+  };
+  const origGetById = globalThis.document.getElementById;
+  globalThis.document.getElementById = (id) => {
+    if (id === 'sidebar-list') return mockList;
+    return null;
+  };
+
+  // Set up single source
+  app._setSources([
+    { url: '', name: 'Laptop', type: 'local', status: 'authenticated', backoffMs: 2000 },
+  ]);
+
+  app._setViewMode('fullscreen');
+  const sessions = [
+    { name: 'alpha', deviceName: 'Laptop', sourceUrl: '', sessionKey: '::alpha', snapshot: '', bell: { unseen_count: 0 } },
+    { name: 'beta', deviceName: 'Laptop', sourceUrl: '', sessionKey: '::beta', snapshot: '', bell: { unseen_count: 0 } },
+  ];
+  app.renderSidebar(sessions, null);
+
+  assert.ok(!capturedHTML.includes('sidebar-device-header'), 'sidebar HTML should NOT contain sidebar-device-header when only one source');
+  assert.ok(capturedHTML.includes('sidebar-item'), 'sidebar HTML should still contain sidebar-item elements');
+
+  // Cleanup
+  app._setSources([]);
+  globalThis.document.getElementById = origGetById;
+  app._setViewMode('grid');
+});