diff --git a/README.md b/README.md
index 024eca9..6bfc6bc 100644
--- a/README.md
+++ b/README.md
@@ -301,6 +301,7 @@ The browser bootstrap includes contacts, calls, messages, mail, invoices, transa
 
 System overlays are available through dedicated preview parameters:
 
+- Lock screen: `http://localhost:5174/?apiPort=3002&lockScreenPreview=1`
 - SIM picker: `http://localhost:5174/?apiPort=3002&simPickerPreview=1`
 - Payphone: `http://localhost:5174/?apiPort=3002&payphonePreview=1` (dial `5551110001` for a connected call or `5550000000` for a busy line)
 
diff --git a/frontend/src/App.vue b/frontend/src/App.vue
index d7f4f4d..348d9f1 100644
--- a/frontend/src/App.vue
+++ b/frontend/src/App.vue
@@ -244,6 +244,9 @@ const PHONE_PORTRAIT_WIDTH = 390
 const PHONE_PORTRAIT_HEIGHT = 844
 const MIN_PRODUCTION_PHONE_ZOOM = 260 / PHONE_PORTRAIT_WIDTH
 const isDevelopment = import.meta.env.DEV
+const developmentParameters = new URLSearchParams(window.location.search)
+const developmentLockScreenPreview =
+  isDevelopment && developmentParameters.has('lockScreenPreview')
 
 const phone = usePhoneStore()
 const account = useAccountStore()
@@ -1177,7 +1180,6 @@ onMounted(() => {
     }
   }, 1000)
   if (isDevelopment) {
-    const developmentParameters = new URLSearchParams(window.location.search)
     void hydrateDevelopmentPhone()
     if (developmentParameters.has('simPickerPreview')) {
       simPicker.value = {
@@ -1251,7 +1253,7 @@ watch(
       }
       return
     }
-    isLocked.value = true
+    isLocked.value = !isDevelopment || developmentLockScreenPreview
     unlockedServicesLoaded.value = false
     controlCenterOpened.value = false
     weather.start()
@@ -1268,7 +1270,8 @@ watch(
       startPasscodeLock(passcodeRetrySeconds.value)
     }
     phone.setLaunchOrigin(null)
-    void router.replace('/')
+    if (isLocked.value) void router.replace('/')
+    else loadUnlockedPhoneData()
   },
 )
 
diff --git a/frontend/src/AppDevelopmentPreview.contract.test.ts b/frontend/src/AppDevelopmentPreview.contract.test.ts
new file mode 100644
index 0000000..c37a00b
--- /dev/null
+++ b/frontend/src/AppDevelopmentPreview.contract.test.ts
@@ -0,0 +1,21 @@
+import { readFileSync } from 'node:fs'
+
+import { describe, expect, it } from 'vitest'
+
+const source = readFileSync(new URL('./App.vue', import.meta.url), 'utf8')
+
+describe('browser development preview contract', () => {
+  it('starts unlocked while preserving an explicit lock screen preview', () => {
+    expect(source).toContain(
+      "developmentParameters.has('lockScreenPreview')",
+    )
+    expect(source).toContain(
+      'isLocked.value = !isDevelopment || developmentLockScreenPreview',
+    )
+  })
+
+  it('loads authenticated app data without replacing direct app routes', () => {
+    expect(source).toContain("if (isLocked.value) void router.replace('/')")
+    expect(source).toContain('else loadUnlockedPhoneData()')
+  })
+})