diff --git a/app/src/main/java/se/ajpanton/notificationlog/MainActivity.kt b/app/src/main/java/se/ajpanton/notificationlog/MainActivity.kt
index 38d67b3..8b86c79 100644
--- a/app/src/main/java/se/ajpanton/notificationlog/MainActivity.kt
+++ b/app/src/main/java/se/ajpanton/notificationlog/MainActivity.kt
@@ -1,6 +1,9 @@
 package se.ajpanton.notificationlog
 
 import android.os.Bundle
+import android.hardware.biometrics.BiometricPrompt
+import android.hardware.biometrics.BiometricManager.Authenticators
+import android.os.CancellationSignal
 import android.content.res.Configuration
 import android.view.Menu
 import android.view.MenuItem
@@ -19,11 +22,13 @@ import androidx.fragment.app.commit
 import com.google.android.material.navigation.NavigationView
 import se.ajpanton.notificationlog.databinding.ActivityMainBinding
 import se.ajpanton.notificationlog.settings.LoggingType
+import se.ajpanton.notificationlog.settings.AppLockStore
 
 class MainActivity : AppCompatActivity(), NavigationView.OnNavigationItemSelectedListener {
     private lateinit var binding: ActivityMainBinding
     private lateinit var drawerToggle: ActionBarDrawerToggle
     private var permanentSidebar = false
+    private var needsUnlock = true
     private var currentItemId = R.id.nav_view_logs
     private var drawerNavigationBasePaddingLeft: Int? = null
     private var permanentNavigationBasePaddingLeft: Int? = null
@@ -77,6 +82,27 @@ class MainActivity : AppCompatActivity(), NavigationView.OnNavigationItemSelecte
         super.onSaveInstanceState(outState)
     }
 
+    override fun onResume() {
+        super.onResume()
+        if (needsUnlock && AppLockStore(this).enabled) requestUnlock()
+    }
+
+    override fun onStop() {
+        super.onStop()
+        if (!isChangingConfigurations) needsUnlock = true
+    }
+
+    private fun requestUnlock() {
+        BiometricPrompt.Builder(this)
+            .setTitle("Unlock Notification Log")
+            .setAllowedAuthenticators(Authenticators.BIOMETRIC_STRONG or Authenticators.DEVICE_CREDENTIAL)
+            .build()
+            .authenticate(CancellationSignal(), mainExecutor, object : BiometricPrompt.AuthenticationCallback() {
+                override fun onAuthenticationSucceeded(result: BiometricPrompt.AuthenticationResult?) { needsUnlock = false }
+                override fun onAuthenticationError(errorCode: Int, errString: CharSequence?) { finishAndRemoveTask() }
+            })
+    }
+
     override fun onNavigationItemSelected(item: MenuItem): Boolean {
         if (item.itemId == R.id.nav_settings_header) {
             return false
diff --git a/app/src/main/java/se/ajpanton/notificationlog/SettingsFragment.kt b/app/src/main/java/se/ajpanton/notificationlog/SettingsFragment.kt
index ef6d7ef..df1c3e0 100644
--- a/app/src/main/java/se/ajpanton/notificationlog/SettingsFragment.kt
+++ b/app/src/main/java/se/ajpanton/notificationlog/SettingsFragment.kt
@@ -11,6 +11,7 @@ import se.ajpanton.notificationlog.settings.LogViewSettingsStore
 import se.ajpanton.notificationlog.settings.TimestampZone
 import se.ajpanton.notificationlog.settings.LoggingType
 import se.ajpanton.notificationlog.settings.LoggingRuleStore
+import se.ajpanton.notificationlog.settings.AppLockStore
 import com.google.android.material.dialog.MaterialAlertDialogBuilder
 
 class SettingsFragment : Fragment(R.layout.fragment_settings) {
@@ -46,6 +47,9 @@ class SettingsFragment : Fragment(R.layout.fragment_settings) {
             }
         }
         binding!!.copyEventSettings.setOnClickListener { chooseCopySource() }
+        val lockStore = AppLockStore(requireContext())
+        binding!!.appLock.isChecked = lockStore.enabled
+        binding!!.appLock.setOnCheckedChangeListener { _, enabled -> lockStore.enabled = enabled }
     }
     override fun onDestroyView() { binding = null; super.onDestroyView() }
 
diff --git a/app/src/main/java/se/ajpanton/notificationlog/settings/AppLockStore.kt b/app/src/main/java/se/ajpanton/notificationlog/settings/AppLockStore.kt
new file mode 100644
index 0000000..39dd867
--- /dev/null
+++ b/app/src/main/java/se/ajpanton/notificationlog/settings/AppLockStore.kt
@@ -0,0 +1,10 @@
+package se.ajpanton.notificationlog.settings
+
+import android.content.Context
+
+class AppLockStore(context: Context) {
+    private val prefs = context.getSharedPreferences("app-lock", Context.MODE_PRIVATE)
+    var enabled: Boolean
+        get() = prefs.getBoolean("enabled", false)
+        set(value) = prefs.edit().putBoolean("enabled", value).apply()
+}
diff --git a/app/src/main/res/layout/fragment_settings.xml b/app/src/main/res/layout/fragment_settings.xml
index da09ba8..0ee1f05 100644
--- a/app/src/main/res/layout/fragment_settings.xml
+++ b/app/src/main/res/layout/fragment_settings.xml
@@ -1,2 +1,2 @@
 <?xml version="1.0" encoding="utf-8"?>
-<ScrollView xmlns:android="http://schemas.android.com/apk/res/android" android:layout_width="match_parent" android:layout_height="match_parent"><LinearLayout android:layout_width="match_parent" android:layout_height="wrap_content" android:orientation="vertical" android:padding="@dimen/page_padding"><TextView android:layout_width="match_parent" android:layout_height="wrap_content" android:text="Settings" android:textAppearance="?attr/textAppearanceHeadline5"/><TextView android:layout_width="match_parent" android:layout_height="wrap_content" android:layout_marginTop="24dp" android:text="Show on each log line"/><LinearLayout android:id="@+id/field_toggles" android:layout_width="match_parent" android:layout_height="wrap_content" android:orientation="vertical"/><TextView android:layout_width="match_parent" android:layout_height="wrap_content" android:layout_marginTop="24dp" android:text="Timestamp timezone"/><Spinner android:id="@+id/timezone" android:layout_width="match_parent" android:layout_height="wrap_content"/><Button android:id="@+id/copy_event_settings" android:layout_width="wrap_content" android:layout_height="wrap_content" android:layout_marginTop="24dp" android:text="Copy settings"/></LinearLayout></ScrollView>
+<ScrollView xmlns:android="http://schemas.android.com/apk/res/android" xmlns:app="http://schemas.android.com/apk/res-auto" android:layout_width="match_parent" android:layout_height="match_parent"><LinearLayout android:layout_width="match_parent" android:layout_height="wrap_content" android:orientation="vertical" android:padding="@dimen/page_padding"><TextView android:layout_width="match_parent" android:layout_height="wrap_content" android:text="Settings" android:textAppearance="?attr/textAppearanceHeadline5"/><TextView android:layout_width="match_parent" android:layout_height="wrap_content" android:layout_marginTop="24dp" android:text="Show on each log line"/><LinearLayout android:id="@+id/field_toggles" android:layout_width="match_parent" android:layout_height="wrap_content" android:orientation="vertical"/><TextView android:layout_width="match_parent" android:layout_height="wrap_content" android:layout_marginTop="24dp" android:text="Timestamp timezone"/><Spinner android:id="@+id/timezone" android:layout_width="match_parent" android:layout_height="wrap_content"/><com.google.android.material.switchmaterial.SwitchMaterial android:id="@+id/app_lock" android:layout_width="match_parent" android:layout_height="wrap_content" android:layout_marginTop="24dp" android:text="Lock app with phone unlock"/><Button android:id="@+id/copy_event_settings" android:layout_width="wrap_content" android:layout_height="wrap_content" android:layout_marginTop="24dp" android:text="Copy settings"/></LinearLayout></ScrollView>