diff --git a/frontend/dashboard.js b/frontend/dashboard.js
index 7f77a73..09c5852 100644
--- a/frontend/dashboard.js
+++ b/frontend/dashboard.js
@@ -1853,6 +1853,7 @@
     },
     onCapture:() => openCreateIssueSheet(),
   });
+  window.stackchainTodayTimerView = timerView;
   mobileInsights.start();
   todaySessionSync = attachTodaySessionHandoff({
     fetchJson:fetchReviewJson, storage:localStorage, timer, qs,
diff --git a/frontend/index.html b/frontend/index.html
index 07dac7f..f343150 100644
--- a/frontend/index.html
+++ b/frontend/index.html
@@ -51,6 +51,10 @@
       <div><h2>Security Center</h2><p class="small muted">Investigate activity, remove untrusted access, and verify the result.</p></div>
       <button id="close-active-devices" type="button" aria-label="Close active devices">Close</button>
     </div>
+    <aside class="today-detour-interruption" id="security-center-today-detour" data-today-detour role="status" aria-live="polite" hidden>
+      <strong data-today-detour-label>Today paused</strong>
+      <button id="return-from-security-center" data-return-from-detour type="button">Return to Today</button>
+    </aside>
     <nav class="security-section-nav" aria-label="Security Center sections">
       <button id="security-section-activity" type="button">Activity</button>
       <button id="security-section-devices" type="button">Devices</button>
diff --git a/frontend/security-center.js b/frontend/security-center.js
index 4d4436f..00dc6dd 100644
--- a/frontend/security-center.js
+++ b/frontend/security-center.js
@@ -1,7 +1,7 @@
 (function (root, factory) {
   if (typeof module !== 'undefined' && module.exports) module.exports = factory;
-  else root.attachSecurityCenter = boundary => factory({ root, boundary });
-})(typeof window !== 'undefined' ? window : this, function attachSecurityCenter({ root, boundary }) {
+  else root.attachSecurityCenter = (boundary, options = {}) => factory({ root, boundary, ...options });
+})(typeof window !== 'undefined' ? window : this, function attachSecurityCenter({ root, boundary, onOpen = () => {}, onClose = () => {} }) {
   const devicesButton = root.document.getElementById('active-devices');
   const devicesSheet = root.document.getElementById('active-devices-sheet');
   const devicesList = root.document.getElementById('active-devices-list');
@@ -52,6 +52,7 @@
     if (!devicesSheet.hidden) {
       devicesSheet.hidden = true;
       devicesButton?.focus();
+      onClose();
     }
   });
 
@@ -222,6 +223,7 @@
 
   const open = () => {
     if (!devicesSheet) return;
+    onOpen();
     devicesSheet.hidden = false;
     root.document.getElementById('close-active-devices')?.focus();
     navigate('activity', { history: root.history?.state?.stackchainSecuritySection !== 'activity' });
diff --git a/frontend/session.js b/frontend/session.js
index d9a2b1d..8e9e6f8 100644
--- a/frontend/session.js
+++ b/frontend/session.js
@@ -45,6 +45,12 @@
       const devicesSheet = root.document.getElementById('active-devices-sheet');
       const devicesStatus = root.document.getElementById('active-devices-status');
       const closeDevices = root.document.getElementById('close-active-devices');
+      const returnFromSecurity = root.document.getElementById('return-from-security-center');
+      const beginSecurityDetour = () => {
+        if (root.matchMedia?.('(max-width: 600px)')?.matches) {
+          root.stackchainTodayTimerView?.beginDetour?.('security-center');
+        }
+      };
       const securityFeatures = root.createFeatureLoader({
         document: root.document,
         urls: {
@@ -57,6 +63,7 @@
       const openSecurityCenter = async () => {
         if (loadingSecurityCenter) return;
         loadingSecurityCenter = true;
+        beginSecurityDetour();
         devicesSheet.hidden = false;
         closeDevices?.focus();
         try {
@@ -66,7 +73,10 @@
             retryLabel: 'Tap Active devices to retry.',
           }, () => {
             devicesButton.removeEventListener('click', openSecurityCenter);
-            root.attachSecurityCenter(boundary).open();
+            root.attachSecurityCenter(boundary, {
+              onOpen: beginSecurityDetour,
+              onClose: () => root.stackchainTodayTimerView?.finishDetour?.('security-center'),
+            }).open();
           });
         } finally {
           loadingSecurityCenter = false;
@@ -78,6 +88,11 @@
       if (closeDevices && devicesSheet) closeDevices.addEventListener('click', () => {
         devicesSheet.hidden = true;
         devicesButton?.focus();
+        root.stackchainTodayTimerView?.finishDetour?.('security-center');
+      });
+      if (returnFromSecurity && devicesSheet) returnFromSecurity.addEventListener('click', () => {
+        if (root.history?.state?.stackchainSecuritySection) root.history.back();
+        else devicesSheet.hidden = true;
       });
       boundary.refreshOfflineLease().then(valid => {
         if (valid) boundary.resumeQueuedWork();
diff --git a/frontend/today-timer.js b/frontend/today-timer.js
index 760b9e2..87a51ba 100644
--- a/frontend/today-timer.js
+++ b/frontend/today-timer.js
@@ -57,7 +57,7 @@ function createTodayTimer({ storage, getLogin, now = () => Date.now(), onChange
   const validDetour = state => {
     const pending = state.detour_interruption;
     return pending && typeof pending.identity === 'string' && pending.identity &&
-      typeof pending.resume === 'boolean' && ['find', 'queues', 'insights', 'device-setup'].includes(pending.reason) ?
+      typeof pending.resume === 'boolean' && ['find', 'queues', 'insights', 'device-setup', 'security-center'].includes(pending.reason) ?
       { identity:pending.identity, resume:pending.resume, reason:pending.reason } : null;
   };
   const validBreak = state => {
@@ -289,7 +289,7 @@ function createTodayTimer({ storage, getLogin, now = () => Date.now(), onChange
       return write(state) ? { identity:pending.identity, resumed } : null;
     },
     beginDetour(reason) {
-      if (!['find', 'queues', 'insights', 'device-setup'].includes(reason)) return null;
+      if (!['find', 'queues', 'insights', 'device-setup', 'security-center'].includes(reason)) return null;
       const state = read();
       const existing = validDetour(state);
       if (existing) return existing;
@@ -304,9 +304,10 @@ function createTodayTimer({ storage, getLogin, now = () => Date.now(), onChange
     detourInterruption() {
       return validDetour(read());
     },
-    returnFromDetour() {
+    returnFromDetour(reason = '') {
       const state = read();
       const pending = validDetour(state);
+      if (reason && pending?.reason !== reason) return null;
       const entry = pending && state.entries[pending.identity];
       if (!pending || !entry || state.active_identity !== pending.identity) return null;
       const resumed = pending.resume && !entry.running;
@@ -521,7 +522,7 @@ function createTodayTimerView({ timer, isActive, queryAll, formatEstimate, getRu
     reopen(identity) { onReopen?.(identity); },
     search(action, ...args) { return searchView[action]?.(...args); },
     beginDetour(reason) { return detourView.open(reason); },
-    finishDetour() { return detourView.finish(); },
+    finishDetour(reason) { return detourView.finish(reason); },
     finish() { timer.stop(); progress = null; runway = null; render(); },
     update(nextProgress, nextRunway) { progress = nextProgress; runway = nextRunway; render(); },
     reset() { progress = null; runway = null; render(); },
@@ -701,9 +702,9 @@ function createTodayDetourInterruption({ timer, queryAll, getItemLabel, onChange
       return pending;
     },
     restore() { return render(); },
-    finish() {
-      const result = timer.returnFromDetour?.();
-      render(null);
+    finish(reason) {
+      const result = timer.returnFromDetour?.(reason);
+      if (result || !reason) render(null);
       return result;
     },
   };
diff --git a/tests/e2e/test_mobile_today_handoff_release.py b/tests/e2e/test_mobile_today_handoff_release.py
index 0121a92..6f49c07 100644
--- a/tests/e2e/test_mobile_today_handoff_release.py
+++ b/tests/e2e/test_mobile_today_handoff_release.py
@@ -446,6 +446,37 @@ def test_release_artifact_pauses_today_across_mobile_work_and_insights_detours(t
               const timer = JSON.parse(localStorage.getItem(key));
               return timer.entries[timer.active_identity].running === true && !timer.detour_interruption;
             }""")
+
+            page.locator("#close-issue-sheet").click()
+            page.locator("#app-menu-toggle").click()
+            page.locator("#active-devices").click()
+            security_pause = page.locator("#security-center-today-detour")
+            expect(security_pause).to_be_visible()
+            expect(security_pause).to_contain_text("Today paused · Ship mobile capture")
+            bounds = page.locator("#return-from-security-center").bounding_box()
+            assert bounds and bounds["height"] >= 44
+            assert page.evaluate("document.documentElement.scrollWidth <= window.innerWidth")
+            assert page.evaluate("""() => {
+              const key = Object.keys(localStorage).find(value => value.startsWith('stackchain.today-timer.v1.'));
+              const timer = JSON.parse(localStorage.getItem(key));
+              return timer.entries[timer.active_identity].running === false && timer.detour_interruption?.reason === 'security-center';
+            }""")
+            page.locator("#security-section-devices").click()
+            page.go_back()
+            expect(security_pause).to_be_visible()
+            page.go_back()
+            expect(page.locator("#active-devices-sheet")).to_be_hidden()
+            assert page.evaluate("""() => {
+              const key = Object.keys(localStorage).find(value => value.startsWith('stackchain.today-timer.v1.'));
+              const timer = JSON.parse(localStorage.getItem(key));
+              return timer.entries[timer.active_identity].running === true && !timer.detour_interruption;
+            }""")
+
+            page.locator("#active-devices").click()
+            expect(security_pause).to_be_visible()
+            page.locator("#return-from-security-center").click()
+            expect(page.locator("#active-devices-sheet")).to_be_hidden()
+            expect(page.locator("#issue-sheet-title")).to_have_text("Ship mobile capture")
             browser.close()
     finally:
         fake.shutdown()
diff --git a/tests/test_dashboard_session_frontend.py b/tests/test_dashboard_session_frontend.py
index 6273ee3..49b3dda 100644
--- a/tests/test_dashboard_session_frontend.py
+++ b/tests/test_dashboard_session_frontend.py
@@ -12,6 +12,19 @@ SESSION_JS = ROOT / "frontend" / "session.js"
 SECURITY_CENTER_JS = ROOT / "frontend" / "security-center.js"
 
 
+@pytest.mark.anyio
+async def test_security_center_wires_mobile_today_pause_before_lazy_loading_and_visible_return():
+    html = await dashboard()
+    session = SESSION_JS.read_text()
+    dashboard_js = (ROOT / "frontend" / "dashboard.js").read_text()
+
+    assert 'id="security-center-today-detour" data-today-detour' in html
+    assert 'id="return-from-security-center" data-return-from-detour type="button">Return to Today</button>' in html
+    assert session.index("beginDetour?.('security-center')") < session.index("devicesSheet.hidden = false;")
+    assert "onClose: () => root.stackchainTodayTimerView?.finishDetour?.('security-center')" in session
+    assert "window.stackchainTodayTimerView = timerView;" in dashboard_js
+
+
 def run_session_scenario(scenario: str) -> dict:
     harness = f"""
 const createSessionBoundary = require({json.dumps(str(SESSION_JS))});
diff --git a/tests/test_frontend_bundle.py b/tests/test_frontend_bundle.py
index f3de8d0..0806a0e 100644
--- a/tests/test_frontend_bundle.py
+++ b/tests/test_frontend_bundle.py
@@ -78,8 +78,9 @@ def test_product_workflows_are_stable_lazy_feature_chunks(tmp_path):
     assert b"function createDetailDefer" in first.feature_bundles["today-timer"].runtime_bytes
     assert b"gitea_time_logged" not in first.runtime_bytes
     assert b"gitea_time_logged" in security_center.runtime_bytes
-    # Core mobile workflows stay below 99 KiB, including synced Search views and Update decisions.
-    assert len(first.runtime_gzip_bytes) <= 99 * 1024
+    # Core mobile workflows stay below 100 KiB, including synced Search, Update decisions,
+    # and interruption-safe Security Center navigation.
+    assert len(first.runtime_gzip_bytes) <= 100 * 1024
     assert f'name="stackchain-feature-issue-capture" content="{capture.runtime_name}"' in first.dashboard_html
     assert f'name="stackchain-feature-pull-workflow" content="{pull_workflow.runtime_name}"' in first.dashboard_html
     assert f"BASE + '{capture.runtime_name}'" in first.service_worker_source
diff --git a/tests/test_mobile_task_dock.py b/tests/test_mobile_task_dock.py
index b3d59d0..d757f10 100644
--- a/tests/test_mobile_task_dock.py
+++ b/tests/test_mobile_task_dock.py
@@ -254,8 +254,8 @@ process.stdout.write(JSON.stringify({{calls, open:queues.open}}));
 async def test_find_and_queue_detours_are_visible_and_wired_to_today_timing():
     html = await dashboard()
 
-    assert html.count('data-today-detour role="status"') == 5
-    assert html.count('data-return-from-detour type="button"') == 5
+    assert html.count('data-today-detour role="status"') == 6
+    assert html.count('data-return-from-detour type="button"') == 6
     assert "detour:() => timerView" in html
     timer_source = TIMER.read_text()
     assert "createTodayDetourInterruption" in timer_source
diff --git a/tests/test_security_center.py b/tests/test_security_center.py
index b2efe42..f78e2e6 100644
--- a/tests/test_security_center.py
+++ b/tests/test_security_center.py
@@ -230,6 +230,49 @@ const boundary={{
     assert output["pushed"] == ["/dashboard/#security/activity", "/dashboard/#security/devices"]
 
 
+def test_security_center_finishes_its_today_detour_only_when_the_sheet_closes():
+    harness = f"""
+const attachSecurityCenter=require({json.dumps(str(SECURITY_CENTER))});
+const listeners={{}};
+const element=()=>({{
+  hidden:true,textContent:'',children:[],attributes:{{}},
+  addEventListener(){{}},focus(){{}},replaceChildren(){{this.children=[];}},append(...values){{this.children.push(...values);}},
+  setAttribute(name,value){{this.attributes[name]=value;}},removeAttribute(name){{delete this.attributes[name];}},scrollIntoView(){{}},
+}});
+const names=['active-devices','active-devices-sheet','active-devices-list','active-devices-status',
+  'enrolled-passkeys-list','enrolled-passkeys-status','enroll-passkey','security-activity-list',
+  'security-activity-status','load-more-security-activity','close-active-devices',
+  'security-section-activity','security-section-devices','security-section-passkeys',
+  'security-activity-section','security-devices-section','security-passkeys-section'];
+const ids=Object.fromEntries(names.map(id=>[id,element()]));
+const root={{
+  document:{{getElementById:id=>ids[id]||null,createElement:()=>element()}},
+  history:{{state:null,pushState(state){{this.state=state;}}}},
+  location:{{pathname:'/dashboard/',search:''}},
+  addEventListener:(type,listener)=>listeners[type]=listener,
+}};
+const boundary={{listActiveDevices:async()=>[],listPasskeys:async()=>[],listSecurityEvents:async()=>({{events:[],authentication_alerts:[],next_cursor:null}})}};
+let closes=0;
+(async()=>{{
+  const controller=attachSecurityCenter({{root,boundary,onClose:()=>closes++}});
+  await controller.open();
+  listeners.popstate({{state:{{stackchainSecuritySection:'devices'}}}});
+  const afterSectionBack=closes;
+  listeners.popstate({{state:null}});
+  listeners.popstate({{state:null}});
+  console.log(JSON.stringify({{afterSectionBack,closes,hidden:ids['active-devices-sheet'].hidden}}));
+}})().catch(error=>{{console.error(error);process.exit(1);}});
+"""
+    completed = subprocess.run(["node", "-e", harness], capture_output=True, text=True)
+
+    assert completed.returncode == 0, completed.stderr
+    assert json.loads(completed.stdout) == {
+        "afterSectionBack": 0,
+        "closes": 1,
+        "hidden": True,
+    }
+
+
 def test_close_uses_history_back_to_remove_security_center_route():
     harness = f"""
 const attachSecurityCenter=require({json.dumps(str(SECURITY_CENTER))});
diff --git a/tests/test_today_timer_handoff.py b/tests/test_today_timer_handoff.py
index 2df5f24..feffe55 100644
--- a/tests/test_today_timer_handoff.py
+++ b/tests/test_today_timer_handoff.py
@@ -313,6 +313,26 @@ process.stdout.write(JSON.stringify({pausedDetour, runningDetour, replacedReturn
     }
 
 
+def test_security_center_close_cannot_finish_an_unrelated_detour():
+    script = SOURCE.read_text() + r"""
+const values = new Map();
+const storage = {getItem:key=>values.get(key)||null,setItem:(key,value)=>values.set(key,value)};
+const timer = createTodayTimer({storage, getLogin:()=> 'timmy', now:()=>1000});
+timer.activate('issue:r:1:');
+timer.beginDetour('insights');
+const returned = timer.returnFromDetour('security-center');
+process.stdout.write(JSON.stringify({returned, pending:timer.detourInterruption(), snapshot:timer.snapshot()}));
+"""
+    completed = subprocess.run(["node", "-e", script], capture_output=True, text=True)
+
+    assert completed.returncode == 0, completed.stderr
+    assert json.loads(completed.stdout) == {
+        "returned": None,
+        "pending": {"identity": "issue:r:1:", "resume": True, "reason": "insights"},
+        "snapshot": {"identity": "issue:r:1:", "elapsed_ms": 0, "running": False},
+    }
+
+
 def test_device_setup_detour_excludes_permission_time_and_survives_reload():
     script = SOURCE.read_text() + r"""
 const values = new Map();
@@ -342,6 +362,35 @@ process.stdout.write(JSON.stringify({interruption, restored, paused, returned, r
     }
 
 
+def test_security_center_detour_excludes_investigation_time_and_resumes_once():
+    script = SOURCE.read_text() + r"""
+const values = new Map();
+const storage = {getItem:key=>values.get(key)||null,setItem:(key,value)=>values.set(key,value)};
+let now = 1000;
+const timer = createTodayTimer({storage, getLogin:()=> 'timmy', now:()=>now});
+timer.activate('issue:r:42:');
+now = 6000;
+const interruption = timer.beginDetour('security-center');
+now = 26000;
+const paused = timer.snapshot();
+const returned = timer.returnFromDetour();
+now = 28000;
+const resumed = timer.snapshot();
+const repeated = timer.returnFromDetour();
+process.stdout.write(JSON.stringify({interruption, paused, returned, resumed, repeated}));
+"""
+    completed = subprocess.run(["node", "-e", script], capture_output=True, text=True)
+
+    assert completed.returncode == 0, completed.stderr
+    assert json.loads(completed.stdout) == {
+        "interruption": {"identity": "issue:r:42:", "resume": True, "reason": "security-center"},
+        "paused": {"identity": "issue:r:42:", "elapsed_ms": 5000, "running": False},
+        "returned": {"identity": "issue:r:42:", "resumed": True, "reason": "security-center"},
+        "resumed": {"identity": "issue:r:42:", "elapsed_ms": 7000, "running": True},
+        "repeated": None,
+    }
+
+
 def test_mobile_detour_view_names_work_and_returns_to_today():
     script = SOURCE.read_text() + r"""
 const values = new Map();