diff --git a/frontend/security-center.js b/frontend/security-center.js
index a0e2fc1..ff1ada0 100644
--- a/frontend/security-center.js
+++ b/frontend/security-center.js
@@ -19,6 +19,31 @@
     section, root.document.getElementById(`security-${section}-section`),
   ]));
   let activityCursor = null;
+  let backgroundInert = null;
+
+  const backgroundElements = ['header', 'main', '#mobile-task-dock']
+    .map(selector => root.document.querySelector?.(selector))
+    .filter(Boolean);
+  const focusableControls = () => [...(devicesSheet?.querySelectorAll?.(
+    'button:not([disabled]), select:not([disabled]), input:not([disabled]), textarea:not([disabled]), a[href], [tabindex]:not([tabindex="-1"])'
+  ) || [])].filter(control => !control.hidden && !control.disabled);
+  const containBackground = () => {
+    if (!backgroundInert) {
+      backgroundInert = new Map(backgroundElements.map(element => [element, element.inert]));
+    }
+    backgroundInert.forEach((_wasInert, element) => { element.inert = true; });
+  };
+  const releaseBackground = () => {
+    if (!backgroundInert) return;
+    backgroundInert.forEach((wasInert, element) => { element.inert = wasInert; });
+    backgroundInert = null;
+  };
+  const finishClose = () => {
+    devicesSheet.hidden = true;
+    releaseBackground();
+    devicesButton?.focus();
+    onClose();
+  };
 
   const navigate = (section, { history = true } = {}) => {
     if (!sections[section]) section = 'activity';
@@ -43,16 +68,41 @@
   root.document.getElementById('close-active-devices')?.addEventListener('click', () => {
     if (root.history?.state?.stackchainSecuritySection) root.history.back();
   });
-  root.addEventListener?.('popstate', event => {
-    const section = event.state?.stackchainSecuritySection;
+  const handleRouteChange = section => {
     if (section && !devicesSheet.hidden) {
+      containBackground();
       navigate(section, { history: false });
       return;
     }
     if (!devicesSheet.hidden) {
-      devicesSheet.hidden = true;
-      devicesButton?.focus();
-      onClose();
+      finishClose();
+    }
+  };
+  root.addEventListener?.('popstate', event => {
+    handleRouteChange(event.state?.stackchainSecuritySection);
+  });
+  root.addEventListener?.('hashchange', () => {
+    handleRouteChange(root.history?.state?.stackchainSecuritySection);
+  });
+  root.document.addEventListener?.('keydown', event => {
+    if (devicesSheet.hidden) return;
+    if (event.key === 'Escape') {
+      event.preventDefault();
+      if (root.history?.state?.stackchainSecuritySection) root.history.back();
+      else finishClose();
+      return;
+    }
+    if (event.key !== 'Tab') return;
+    const controls = focusableControls();
+    if (!controls.length) return;
+    const first = controls[0];
+    const last = controls[controls.length - 1];
+    if (event.shiftKey && event.target === first) {
+      event.preventDefault();
+      last.focus();
+    } else if (!event.shiftKey && event.target === last) {
+      event.preventDefault();
+      first.focus();
     }
   });
 
@@ -225,6 +275,7 @@
   const open = () => {
     if (!devicesSheet) return;
     onOpen();
+    containBackground();
     devicesSheet.hidden = false;
     root.document.getElementById('close-active-devices')?.focus();
     navigate('activity', { history: root.history?.state?.stackchainSecuritySection !== 'activity' });
diff --git a/tests/e2e/test_mobile_home_bootstrap_release.py b/tests/e2e/test_mobile_home_bootstrap_release.py
index 9c64683..4a19bd1 100644
--- a/tests/e2e/test_mobile_home_bootstrap_release.py
+++ b/tests/e2e/test_mobile_home_bootstrap_release.py
@@ -170,6 +170,25 @@ def test_release_artifact_bootstraps_mobile_home_and_returns_from_insights(
             page.locator("#active-devices").click()
             expect(page.locator("#active-devices-sheet")).to_be_visible()
             expect(page.locator("#security-activity-section")).to_be_visible()
+            expect(page.locator("body > header")).to_have_attribute("inert", "")
+            expect(page.locator("main")).to_have_attribute("inert", "")
+            expect(dock).to_have_attribute("inert", "")
+            expect(page.locator("#close-active-devices")).to_be_focused()
+            expect(page.locator("#active-devices-status")).to_contain_text("active device")
+            expect(page.locator("#enrolled-passkeys-status")).not_to_contain_text("Loading")
+            page.keyboard.press("Shift+Tab")
+            assert page.evaluate(
+                """
+                () => {
+                  const controls = [...document.querySelector('#active-devices-sheet').querySelectorAll(
+                    'button:not([disabled]), select:not([disabled]), input:not([disabled]), textarea:not([disabled]), a[href], [tabindex]:not([tabindex="-1"])'
+                  )].filter(control => !control.hidden);
+                  return document.activeElement === controls.at(-1);
+                }
+                """
+            )
+            page.keyboard.press("Tab")
+            expect(page.locator("#close-active-devices")).to_be_focused()
             security_nav = page.locator(".security-section-nav")
             expect(security_nav).to_be_visible()
             for control in security_nav.locator("button").all():
@@ -179,9 +198,15 @@ def test_release_artifact_bootstraps_mobile_home_and_returns_from_insights(
             expect(page.locator("#security-section-devices")).to_have_attribute("aria-current", "page")
             page.go_back()
             expect(page.locator("#security-section-activity")).to_have_attribute("aria-current", "page")
+            expect(page.locator("body > header")).to_have_attribute("inert", "")
+            expect(page.locator("main")).to_have_attribute("inert", "")
+            expect(dock).to_have_attribute("inert", "")
             page.go_back()
             expect(page.locator("#active-devices-sheet")).to_be_hidden()
             expect(page.locator("#active-devices")).to_be_focused()
+            expect(page.locator("body > header")).not_to_have_attribute("inert", "")
+            expect(page.locator("main")).not_to_have_attribute("inert", "")
+            expect(dock).not_to_have_attribute("inert", "")
 
             assert len(workspace_requests) == 1, workspace_requests
             assert page.evaluate("document.documentElement.scrollWidth <= window.innerWidth")
diff --git a/tests/test_security_center.py b/tests/test_security_center.py
index f78e2e6..02e225b 100644
--- a/tests/test_security_center.py
+++ b/tests/test_security_center.py
@@ -304,3 +304,139 @@ const boundary={{listActiveDevices:async()=>[],listPasskeys:async()=>[],listSecu
     )
 
     assert json.loads(completed.stdout) == {"backs": 1}
+
+
+def test_security_center_contains_focus_and_restores_prior_background_state_on_final_back():
+    harness = f"""
+const attachSecurityCenter=require({json.dumps(str(SECURITY_CENTER))});
+const listeners={{}};
+const element=(id='', inert=false)=>({{
+  id, inert, hidden:false, disabled:false, textContent:'', children:[], attributes:{{}},
+  addEventListener(type,listener){{(this.listeners ||= {{}})[type]=listener;}},
+  focus(){{focused=this;}}, replaceChildren(){{this.children=[];}},
+  append(...values){{this.children.push(...values);}},
+  setAttribute(name,value){{this.attributes[name]=value;}}, removeAttribute(name){{delete this.attributes[name];}},
+  scrollIntoView(){{}},
+}});
+let focused=null;
+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(id)]));
+ids['active-devices-sheet'].hidden=true;
+const header=element('header');
+const main=element('main', true);
+const dock=element('mobile-task-dock');
+const dynamicAction=element('revoke-lost-phone');
+const hiddenAction=element('hidden-action'); hiddenAction.hidden=true;
+const disabledAction=element('disabled-action'); disabledAction.disabled=true;
+ids['active-devices-sheet'].querySelectorAll=()=>[
+  ids['close-active-devices'], dynamicAction, hiddenAction, disabledAction,
+];
+const documentListeners={{}};
+const root={{
+  document:{{
+    getElementById:id=>ids[id]||null, createElement:()=>element(),
+    querySelector:selector=>({{'header':header,'main':main,'#mobile-task-dock':dock}})[selector]||null,
+    addEventListener:(type,listener)=>documentListeners[type]=listener,
+  }},
+  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}})}};
+(async()=>{{
+  const controller=attachSecurityCenter({{root,boundary}});
+  await controller.open();
+  const opened={{inert:[header.inert,main.inert,dock.inert],focused:focused?.id}};
+  let shiftPrevented=false;
+  documentListeners.keydown({{key:'Tab',shiftKey:true,target:ids['close-active-devices'],preventDefault(){{shiftPrevented=true;}}}});
+  const afterShift=focused?.id;
+  let tabPrevented=false;
+  documentListeners.keydown({{key:'Tab',shiftKey:false,target:dynamicAction,preventDefault(){{tabPrevented=true;}}}});
+  const afterTab=focused?.id;
+  controller.navigate('devices');
+  header.inert=false; // An earlier popstate listener released its own overlay background.
+  listeners.popstate({{state:{{stackchainSecuritySection:'activity'}}}});
+  header.inert=false; // That listener also reacts to the resulting hashchange.
+  root.history.state={{stackchainSecuritySection:'activity'}};
+  listeners.hashchange({{}});
+  const sectionBack={{hidden:ids['active-devices-sheet'].hidden,inert:[header.inert,main.inert,dock.inert]}};
+  root.history.state=null;
+  listeners.popstate({{state:null}});
+  console.log(JSON.stringify({{
+    opened,shiftPrevented,afterShift,tabPrevented,afterTab,sectionBack,
+    closed:{{hidden:ids['active-devices-sheet'].hidden,inert:[header.inert,main.inert,dock.inert],focused:focused?.id}},
+  }}));
+}})().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) == {
+        "opened": {"inert": [True, True, True], "focused": "close-active-devices"},
+        "shiftPrevented": True,
+        "afterShift": "revoke-lost-phone",
+        "tabPrevented": True,
+        "afterTab": "close-active-devices",
+        "sectionBack": {"hidden": False, "inert": [True, True, True]},
+        "closed": {
+            "hidden": True,
+            "inert": [False, True, False],
+            "focused": "active-devices",
+        },
+    }
+
+
+def test_escape_closes_security_center_through_history_and_releases_background():
+    harness = f"""
+const attachSecurityCenter=require({json.dumps(str(SECURITY_CENTER))});
+const windowListeners={{}};
+const documentListeners={{}};
+const element=(id='')=>({{
+  id,inert:false,hidden:false,disabled:false,textContent:'',children:[],attributes:{{}},
+  addEventListener(){{}},focus(){{focused=this.id;}},replaceChildren(){{this.children=[];}},
+  append(...values){{this.children.push(...values);}},setAttribute(){{}},removeAttribute(){{}},scrollIntoView(){{}},
+}});
+let focused='';
+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'];
+const ids=Object.fromEntries(names.map(id=>[id,element(id)]));
+ids['active-devices-sheet'].hidden=true;
+ids['active-devices-sheet'].querySelectorAll=()=>[ids['close-active-devices']];
+const header=element('header');
+let backs=0;
+const root={{
+  document:{{
+    getElementById:id=>ids[id]||null,createElement:()=>element(),
+    querySelector:selector=>selector==='header'?header:null,
+    addEventListener:(type,listener)=>documentListeners[type]=listener,
+  }},
+  history:{{state:null,pushState(state){{this.state=state;}},back(){{backs++;}}}},
+  location:{{pathname:'/dashboard/',search:''}},
+  addEventListener:(type,listener)=>windowListeners[type]=listener,
+}};
+const boundary={{listActiveDevices:async()=>[],listPasskeys:async()=>[],listSecurityEvents:async()=>({{events:[],authentication_alerts:[],next_cursor:null}})}};
+(async()=>{{
+  await attachSecurityCenter({{root,boundary}}).open();
+  let prevented=false;
+  documentListeners.keydown({{key:'Escape',preventDefault(){{prevented=true;}}}});
+  const requested={{backs,prevented,hidden:ids['active-devices-sheet'].hidden,inert:header.inert}};
+  windowListeners.popstate({{state:null}});
+  console.log(JSON.stringify({{requested,closed:{{hidden:ids['active-devices-sheet'].hidden,inert:header.inert,focused}}}}));
+}})().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) == {
+        "requested": {"backs": 1, "prevented": True, "hidden": False, "inert": True},
+        "closed": {"hidden": True, "inert": False, "focused": "active-devices"},
+    }