diff --git a/app/src/main/AndroidManifest.xml b/app/src/main/AndroidManifest.xml
index 91dfc6ec..3820008d 100644
--- a/app/src/main/AndroidManifest.xml
+++ b/app/src/main/AndroidManifest.xml
@@ -21,7 +21,7 @@
 
     <uses-permission android:name="android.permission.READ_CONTACTS" />
     <uses-permission
-        android:name="android.permission.USE_FINGERPRINT"
+        android:name="android.permission.USE_BIOMETRIC"
         tools:node="remove" />
 
     <queries>
@@ -55,9 +55,9 @@
             android:name=".activities.ThreadActivity"
             android:configChanges="orientation"
             android:exported="false"
+            android:launchMode="singleTop"
             android:parentActivityName=".activities.MainActivity"
-            android:windowSoftInputMode="adjustResize"
-            android:launchMode="singleTop" />
+            android:windowSoftInputMode="adjustResize" />
 
         <activity
             android:name=".activities.NewConversationActivity"
diff --git a/app/src/main/kotlin/com/simplemobiletools/smsmessenger/activities/MainActivity.kt b/app/src/main/kotlin/com/simplemobiletools/smsmessenger/activities/MainActivity.kt
index 5a748a51..1204d748 100644
--- a/app/src/main/kotlin/com/simplemobiletools/smsmessenger/activities/MainActivity.kt
+++ b/app/src/main/kotlin/com/simplemobiletools/smsmessenger/activities/MainActivity.kt
@@ -50,6 +50,7 @@ class MainActivity : SimpleActivity() {
     private var lastSearchedText = ""
     private var bus: EventBus? = null
     private val smsExporter by lazy { MessagesExporter(this) }
+    private var wasProtectionHandled = false
 
     @SuppressLint("InlinedApi")
     override fun onCreate(savedInstanceState: Bundle?) {
@@ -62,31 +63,19 @@ class MainActivity : SimpleActivity() {
 
         updateMaterialActivityViews(main_coordinator, conversations_list, useTransparentNavigation = true, useTopSearchMenu = true)
 
-        if (checkAppSideloading()) {
-            return
+        if (savedInstanceState == null) {
+            handleAppPasswordProtection {
+                wasProtectionHandled = it
+                if (it) {
+                    loadMessages()
+                } else {
+                    finish()
+                }
+            }
         }
 
-        if (isQPlus()) {
-            val roleManager = getSystemService(RoleManager::class.java)
-            if (roleManager!!.isRoleAvailable(RoleManager.ROLE_SMS)) {
-                if (roleManager.isRoleHeld(RoleManager.ROLE_SMS)) {
-                    askPermissions()
-                } else {
-                    val intent = roleManager.createRequestRoleIntent(RoleManager.ROLE_SMS)
-                    startActivityForResult(intent, MAKE_DEFAULT_APP_REQUEST)
-                }
-            } else {
-                toast(R.string.unknown_error_occurred)
-                finish()
-            }
-        } else {
-            if (Telephony.Sms.getDefaultSmsPackage(this) == packageName) {
-                askPermissions()
-            } else {
-                val intent = Intent(Telephony.Sms.Intents.ACTION_CHANGE_DEFAULT)
-                intent.putExtra(Telephony.Sms.Intents.EXTRA_PACKAGE_NAME, packageName)
-                startActivityForResult(intent, MAKE_DEFAULT_APP_REQUEST)
-            }
+        if (checkAppSideloading()) {
+            return
         }
 
         clearAllMessagesIfNeeded()
@@ -140,6 +129,29 @@ class MainActivity : SimpleActivity() {
         }
     }
 
+    override fun onSaveInstanceState(outState: Bundle) {
+        super.onSaveInstanceState(outState)
+        outState.putBoolean(WAS_PROTECTION_HANDLED, wasProtectionHandled)
+    }
+
+    override fun onRestoreInstanceState(savedInstanceState: Bundle) {
+        super.onRestoreInstanceState(savedInstanceState)
+        wasProtectionHandled = savedInstanceState.getBoolean(WAS_PROTECTION_HANDLED, false)
+
+        if (!wasProtectionHandled) {
+            handleAppPasswordProtection {
+                wasProtectionHandled = it
+                if (it) {
+                    loadMessages()
+                } else {
+                    finish()
+                }
+            }
+        } else {
+            loadMessages()
+        }
+    }
+
     private fun setupOptionsMenu() {
         main_menu.getToolbar().inflateMenu(R.menu.menu_main)
         main_menu.toggleHideOnScroll(true)
@@ -205,6 +217,31 @@ class MainActivity : SimpleActivity() {
         main_menu.updateColors()
     }
 
+    private fun loadMessages() {
+        if (isQPlus()) {
+            val roleManager = getSystemService(RoleManager::class.java)
+            if (roleManager!!.isRoleAvailable(RoleManager.ROLE_SMS)) {
+                if (roleManager.isRoleHeld(RoleManager.ROLE_SMS)) {
+                    askPermissions()
+                } else {
+                    val intent = roleManager.createRequestRoleIntent(RoleManager.ROLE_SMS)
+                    startActivityForResult(intent, MAKE_DEFAULT_APP_REQUEST)
+                }
+            } else {
+                toast(R.string.unknown_error_occurred)
+                finish()
+            }
+        } else {
+            if (Telephony.Sms.getDefaultSmsPackage(this) == packageName) {
+                askPermissions()
+            } else {
+                val intent = Intent(Telephony.Sms.Intents.ACTION_CHANGE_DEFAULT)
+                intent.putExtra(Telephony.Sms.Intents.EXTRA_PACKAGE_NAME, packageName)
+                startActivityForResult(intent, MAKE_DEFAULT_APP_REQUEST)
+            }
+        }
+    }
+
     // while SEND_SMS and READ_SMS permissions are mandatory, READ_CONTACTS is optional. If we don't have it, we just won't be able to show the contact name in some cases
     private fun askPermissions() {
         handlePermission(PERMISSION_READ_SMS) {
@@ -410,6 +447,7 @@ class MainActivity : SimpleActivity() {
             val conversation = any as Conversation
             putExtra(THREAD_ID, conversation.threadId)
             putExtra(THREAD_TITLE, conversation.title)
+            putExtra(WAS_PROTECTION_HANDLED, wasProtectionHandled)
             startActivity(this)
         }
     }
@@ -636,6 +674,7 @@ class MainActivity : SimpleActivity() {
                     showErrorToast(e)
                 }
             }
+
             else -> toast(R.string.invalid_file_format)
         }
     }
diff --git a/app/src/main/kotlin/com/simplemobiletools/smsmessenger/activities/SettingsActivity.kt b/app/src/main/kotlin/com/simplemobiletools/smsmessenger/activities/SettingsActivity.kt
index fc86ece8..d97e67d0 100644
--- a/app/src/main/kotlin/com/simplemobiletools/smsmessenger/activities/SettingsActivity.kt
+++ b/app/src/main/kotlin/com/simplemobiletools/smsmessenger/activities/SettingsActivity.kt
@@ -5,9 +5,7 @@ import android.content.Intent
 import android.os.Build
 import android.os.Bundle
 import com.simplemobiletools.commons.activities.ManageBlockedNumbersActivity
-import com.simplemobiletools.commons.dialogs.ChangeDateTimeFormatDialog
-import com.simplemobiletools.commons.dialogs.FeatureLockedDialog
-import com.simplemobiletools.commons.dialogs.RadioGroupDialog
+import com.simplemobiletools.commons.dialogs.*
 import com.simplemobiletools.commons.extensions.*
 import com.simplemobiletools.commons.helpers.*
 import com.simplemobiletools.commons.models.RadioItem
@@ -49,6 +47,7 @@ class SettingsActivity : SimpleActivity() {
         setupGroupMessageAsMMS()
         setupLockScreenVisibility()
         setupMMSFileSizeLimit()
+        setupAppPasswordProtection()
         updateTextColors(settings_nested_scrollview)
 
         if (blockedNumbersAtPause != -1 && blockedNumbersAtPause != getBlockedNumbers().hashCode()) {
@@ -59,7 +58,8 @@ class SettingsActivity : SimpleActivity() {
             settings_color_customization_section_label,
             settings_general_settings_label,
             settings_outgoing_messages_label,
-            settings_notifications_label
+            settings_notifications_label,
+            settings_security_label
         ).forEach {
             it.setTextColor(getProperPrimaryColor())
         }
@@ -244,6 +244,28 @@ class SettingsActivity : SimpleActivity() {
         }
     }
 
+    private fun setupAppPasswordProtection() {
+        settings_app_password_protection.isChecked = config.isAppPasswordProtectionOn
+        settings_app_password_protection_holder.setOnClickListener {
+            val tabToShow = if (config.isAppPasswordProtectionOn) config.appProtectionType else SHOW_ALL_TABS
+            SecurityDialog(this, config.appPasswordHash, tabToShow) { hash, type, success ->
+                if (success) {
+                    val hasPasswordProtection = config.isAppPasswordProtectionOn
+                    settings_app_password_protection.isChecked = !hasPasswordProtection
+                    config.isAppPasswordProtectionOn = !hasPasswordProtection
+                    config.appPasswordHash = if (hasPasswordProtection) "" else hash
+                    config.appProtectionType = type
+
+                    if (config.isAppPasswordProtectionOn) {
+                        val confirmationTextId = if (config.appProtectionType == PROTECTION_FINGERPRINT)
+                            R.string.fingerprint_setup_successfully else R.string.protection_setup_successfully
+                        ConfirmationDialog(this, "", confirmationTextId, R.string.ok, 0) { }
+                    }
+                }
+            }
+        }
+    }
+
     private fun getMMSFileLimitText() = getString(
         when (config.mmsFileSizeLimit) {
             FILE_SIZE_100_KB -> R.string.mms_file_size_limit_100kb
diff --git a/app/src/main/kotlin/com/simplemobiletools/smsmessenger/activities/ThreadActivity.kt b/app/src/main/kotlin/com/simplemobiletools/smsmessenger/activities/ThreadActivity.kt
index 6a116d02..08f251ac 100644
--- a/app/src/main/kotlin/com/simplemobiletools/smsmessenger/activities/ThreadActivity.kt
+++ b/app/src/main/kotlin/com/simplemobiletools/smsmessenger/activities/ThreadActivity.kt
@@ -101,6 +101,7 @@ class ThreadActivity : SimpleActivity() {
     private var loadingOlderMessages = false
     private var allMessagesFetched = false
     private var oldestMessageDate = -1
+    private var wasProtectionHandled = false
 
     private var isScheduledMessage: Boolean = false
     private var scheduledMessage: Message? = null
@@ -111,7 +112,7 @@ class ThreadActivity : SimpleActivity() {
     override fun onNewIntent(intent: Intent?) {
         super.onNewIntent(intent)
         finish()
-        startActivity(intent)  
+        startActivity(intent)
     }
 
     override fun onCreate(savedInstanceState: Bundle?) {
@@ -136,28 +137,23 @@ class ThreadActivity : SimpleActivity() {
         intent.getStringExtra(THREAD_TITLE)?.let {
             thread_toolbar.title = it
         }
+        wasProtectionHandled = intent.getBooleanExtra(WAS_PROTECTION_HANDLED, false)
 
         bus = EventBus.getDefault()
         bus!!.register(this)
-        handlePermission(PERMISSION_READ_PHONE_STATE) { granted ->
-            if (granted) {
-                setupButtons()
-                setupConversation()
-                setupCachedMessages {
-                    val searchedMessageId = intent.getLongExtra(SEARCHED_MESSAGE_ID, -1L)
-                    intent.removeExtra(SEARCHED_MESSAGE_ID)
-                    if (searchedMessageId != -1L) {
-                        val index = threadItems.indexOfFirst { (it as? Message)?.id == searchedMessageId }
-                        if (index != -1) {
-                            thread_messages_list.smoothScrollToPosition(index)
-                        }
-                    }
 
-                    setupThread()
-                    setupScrollFab()
+        if (savedInstanceState == null) {
+            if (!wasProtectionHandled) {
+                handleAppPasswordProtection {
+                    wasProtectionHandled = it
+                    if (it) {
+                        loadConversation()
+                    } else {
+                        finish()
+                    }
                 }
             } else {
-                finish()
+                loadConversation()
             }
         }
 
@@ -221,6 +217,29 @@ class ThreadActivity : SimpleActivity() {
         bus?.unregister(this)
     }
 
+    override fun onSaveInstanceState(outState: Bundle) {
+        super.onSaveInstanceState(outState)
+        outState.putBoolean(WAS_PROTECTION_HANDLED, wasProtectionHandled)
+    }
+
+    override fun onRestoreInstanceState(savedInstanceState: Bundle) {
+        super.onRestoreInstanceState(savedInstanceState)
+        wasProtectionHandled = savedInstanceState.getBoolean(WAS_PROTECTION_HANDLED, false)
+
+        if (!wasProtectionHandled) {
+            handleAppPasswordProtection {
+                wasProtectionHandled = it
+                if (it) {
+                    loadConversation()
+                } else {
+                    finish()
+                }
+            }
+        } else {
+            loadConversation()
+        }
+    }
+
     private fun refreshMenuItems() {
         val firstPhoneNumber = participants.firstOrNull()?.phoneNumbers?.firstOrNull()?.value
         thread_toolbar.menu.apply {
@@ -546,6 +565,30 @@ class ThreadActivity : SimpleActivity() {
         }
     }
 
+    private fun loadConversation() {
+        handlePermission(PERMISSION_READ_PHONE_STATE) { granted ->
+            if (granted) {
+                setupButtons()
+                setupConversation()
+                setupCachedMessages {
+                    val searchedMessageId = intent.getLongExtra(SEARCHED_MESSAGE_ID, -1L)
+                    intent.removeExtra(SEARCHED_MESSAGE_ID)
+                    if (searchedMessageId != -1L) {
+                        val index = threadItems.indexOfFirst { (it as? Message)?.id == searchedMessageId }
+                        if (index != -1) {
+                            thread_messages_list.smoothScrollToPosition(index)
+                        }
+                    }
+
+                    setupThread()
+                    setupScrollFab()
+                }
+            } else {
+                finish()
+            }
+        }
+    }
+
     private fun setupConversation() {
         ensureBackgroundThread {
             conversation = conversationsDB.getConversationWithThreadId(threadId)
diff --git a/app/src/main/res/layout/activity_settings.xml b/app/src/main/res/layout/activity_settings.xml
index 7083d0c3..99dfaa9b 100644
--- a/app/src/main/res/layout/activity_settings.xml
+++ b/app/src/main/res/layout/activity_settings.xml
@@ -341,6 +341,32 @@
                     tools:text="@string/mms_file_size_limit_none" />
 
             </RelativeLayout>
+
+            <include
+                android:id="@+id/settings_outgoing_messages_divider"
+                layout="@layout/divider" />
+
+            <TextView
+                android:id="@+id/settings_security_label"
+                style="@style/SettingsSectionLabelStyle"
+                android:layout_width="match_parent"
+                android:layout_height="wrap_content"
+                android:text="@string/security" />
+
+            <RelativeLayout
+                android:id="@+id/settings_app_password_protection_holder"
+                style="@style/SettingsHolderCheckboxStyle"
+                android:layout_width="match_parent"
+                android:layout_height="wrap_content">
+
+                <com.simplemobiletools.commons.views.MyAppCompatCheckbox
+                    android:id="@+id/settings_app_password_protection"
+                    style="@style/SettingsCheckboxStyle"
+                    android:layout_width="match_parent"
+                    android:layout_height="wrap_content"
+                    android:text="@string/password_protect_whole_app" />
+
+            </RelativeLayout>
         </LinearLayout>
     </androidx.core.widget.NestedScrollView>
 </androidx.coordinatorlayout.widget.CoordinatorLayout>