diff --git a/apps/ios/Koins/AppModel.swift b/apps/ios/Koins/AppModel.swift
index 49078e5..96bb202 100644
--- a/apps/ios/Koins/AppModel.swift
+++ b/apps/ios/Koins/AppModel.swift
@@ -15,6 +15,18 @@ final class AppModel: ObservableObject {
   @Published var moneroReady = false
   @Published var moneroAddress: String?
   @Published var moneroAccounts: [MoneroAccount] = []
+  /// Whether the app is behind the biometric lock screen right now.
+  @Published var locked = false
+
+  /// Face ID/Touch ID lock. On by default when the device has biometrics;
+  /// persisted across launches.
+  var faceIDEnabled: Bool {
+    get { UserDefaults.standard.object(forKey: "koins.faceID") as? Bool ?? true }
+    set {
+      UserDefaults.standard.set(newValue, forKey: "koins.faceID")
+      objectWillChange.send()
+    }
+  }
   /// Rough time remaining for the Monero sync, derived from observed block rate.
   @Published var syncEta: String?
 
@@ -41,6 +53,22 @@ final class AppModel: ObservableObject {
 
   var symbol: String { chain.symbol }
 
+  // MARK: - Biometric lock
+
+  func authenticate() async {
+    if await Biometrics.authenticate(reason: "Unlock Koins") {
+      locked = false
+    }
+  }
+
+  /// Requires biometrics for sensitive actions when the lock is enabled; a
+  /// device without biometrics is not asked (the wallet is still usable).
+  func requireAuth(reason: String) async throws {
+    guard faceIDEnabled, Biometrics.isAvailable else { return }
+    let ok = await Biometrics.authenticate(reason: reason)
+    if !ok { throw XRPError.rpc("Authentication failed") }
+  }
+
   // MARK: - Cache
 
   /// Restores the last-known state for the chain on screen instantly; the
@@ -78,6 +106,9 @@ final class AppModel: ObservableObject {
     if xrpWallet != nil || moneroReady {
       chain = xrpWallet != nil ? .xrp : .xmr
     }
+    if xrpWallet != nil || xmrWallet != nil, faceIDEnabled, Biometrics.isAvailable {
+      locked = true
+    }
     showCached(chain)
     await refresh(force: true)
     startAutoRefresh()
@@ -334,6 +365,7 @@ final class AppModel: ObservableObject {
   }
 
   func revealSeed() async throws -> String {
+    try await requireAuth(reason: "Reveal your recovery phrase")
     if chain == .xrp {
       guard let seed = WalletStore.secret(.xrp) else {
         throw XRPError.rpc("No stored secret for this wallet")
@@ -347,6 +379,7 @@ final class AppModel: ObservableObject {
   // MARK: - Sends
 
   func send(to: String, amount: String, tag: String, priority: TransactionPriority) async throws {
+    try await requireAuth(reason: "Authorize this payment")
     let destinationTag = UInt32(tag.trimmingCharacters(in: .whitespaces))
     if chain == .xrp {
       guard let seed = WalletStore.secret(.xrp) else {
diff --git a/apps/ios/Koins/Info.plist b/apps/ios/Koins/Info.plist
index f94fc76..e435c73 100644
--- a/apps/ios/Koins/Info.plist
+++ b/apps/ios/Koins/Info.plist
@@ -25,6 +25,8 @@
 	</dict>
 	<key>NSCameraUsageDescription</key>
 	<string>Scan a QR code to fill in a payment address.</string>
+	<key>NSFaceIDUsageDescription</key>
+	<string>Unlock Koins and approve payments.</string>
 	<key>UILaunchScreen</key>
 	<dict/>
 	<key>UISupportedInterfaceOrientations</key>
diff --git a/apps/ios/Koins/SelfTest.swift b/apps/ios/Koins/SelfTest.swift
index a669647..5ffccf0 100644
--- a/apps/ios/Koins/SelfTest.swift
+++ b/apps/ios/Koins/SelfTest.swift
@@ -290,6 +290,8 @@ enum SelfTest {
     expectTrue("qr not monero", !AddressFormat.isMonero(xrpAddress))
     expectTrue("qr not xrp", !AddressFormat.isXRP(xmrAddress))
 
+    emit("biometrics available=\(Biometrics.isAvailable) label=\(Biometrics.label)")
+
     // secp256k1 signing must produce a low-S DER signature.
     if let keypair = try? XRPKey.keypair(fromSeed: secpSeed),
        let message = Hex.decode(signingHex),
diff --git a/apps/ios/Koins/Support/Biometrics.swift b/apps/ios/Koins/Support/Biometrics.swift
new file mode 100644
index 0000000..1462f12
--- /dev/null
+++ b/apps/ios/Koins/Support/Biometrics.swift
@@ -0,0 +1,25 @@
+import Foundation
+import LocalAuthentication
+
+/// Face ID / Touch ID gating for the app lock and for sensitive actions.
+enum Biometrics {
+  static var isAvailable: Bool {
+    LAContext().canEvaluatePolicy(.deviceOwnerAuthenticationWithBiometrics, error: nil)
+  }
+
+  static var label: String {
+    let context = LAContext()
+    _ = context.canEvaluatePolicy(.deviceOwnerAuthenticationWithBiometrics, error: nil)
+    return context.biometryType == .faceID ? "Face ID" : "Touch ID"
+  }
+
+  /// Biometrics with the system passcode fallback (the alert offers "Use
+  /// Passcode" after a failed face scan).
+  static func authenticate(reason: String) async -> Bool {
+    guard isAvailable else { return false }
+    let context = LAContext()
+    context.localizedCancelTitle = "Cancel"
+    return (try? await context.evaluatePolicy(.deviceOwnerAuthenticationWithBiometrics,
+                                             localizedReason: reason)) ?? false
+  }
+}
\ No newline at end of file
diff --git a/apps/ios/Koins/Views/LockScreen.swift b/apps/ios/Koins/Views/LockScreen.swift
new file mode 100644
index 0000000..dab9cd7
--- /dev/null
+++ b/apps/ios/Koins/Views/LockScreen.swift
@@ -0,0 +1,30 @@
+import SwiftUI
+
+/// Full-screen biometric lock, overlaid on the app whenever `model.locked`.
+struct LockScreen: View {
+  var unlock: () -> Void
+
+  var body: some View {
+    ZStack {
+      Theme.background.ignoresSafeArea()
+      VStack(spacing: 16) {
+        Spacer()
+        Image(systemName: "lock.shield")
+          .font(.system(size: 44, weight: .light))
+          .foregroundStyle(Theme.accent)
+        Text("Koins is locked")
+          .font(.system(size: 22, weight: .bold))
+          .foregroundStyle(Theme.text)
+        Text("Authenticate to continue")
+          .font(.system(size: 13))
+          .foregroundStyle(Theme.muted)
+        Spacer()
+        PrimaryButton(title: "Unlock with \(Biometrics.label)", action: unlock)
+        Spacer()
+      }
+      .padding(24)
+    }
+    .preferredColorScheme(.dark)
+    .task { unlock() }
+  }
+}
\ No newline at end of file
diff --git a/apps/ios/Koins/Views/RootView.swift b/apps/ios/Koins/Views/RootView.swift
index 1c1e450..8cf8b87 100644
--- a/apps/ios/Koins/Views/RootView.swift
+++ b/apps/ios/Koins/Views/RootView.swift
@@ -59,6 +59,13 @@ struct RootView: View {
       .scrollDismissesKeyboard(.interactively)
     }
     .preferredColorScheme(.dark)
+    .overlay {
+      if model.locked, model.faceIDEnabled {
+        LockScreen {
+          Task { await model.authenticate() }
+        }
+      }
+    }
     .task { await model.bootstrap() }
     .sheet(item: $seedBox) { box in
       SeedRevealView(seed: box.seed, symbol: box.symbol) { seedBox = nil }
@@ -67,6 +74,9 @@ struct RootView: View {
       if route == .dashboard { route = .home }
     }
     .onChange(of: scenePhase) { phase in
+      if phase == .background, model.faceIDEnabled, Biometrics.isAvailable {
+        model.locked = true
+      }
       if phase != .active {
         Task { await model.persistWallet() }
       }
@@ -79,6 +89,7 @@ struct HomeView: View {
   @Binding var route: Route
   @State private var showDeleteConfirm = false
   @State private var selectedTransaction: TransactionRecord?
+  @State private var showSettings = false
 
   var body: some View {
     VStack(spacing: 18) {
@@ -104,6 +115,10 @@ struct HomeView: View {
                             symbol: model.symbol,
                             chain: model.chain) { selectedTransaction = nil }
     }
+    .sheet(isPresented: $showSettings) {
+      SettingsView()
+        .environmentObject(model)
+    }
     .confirmationDialog("Delete this wallet?",
                         isPresented: $showDeleteConfirm,
                         titleVisibility: .visible) {
@@ -120,13 +135,26 @@ struct HomeView: View {
   }
 
   private var header: some View {
-    VStack(alignment: .leading, spacing: 4) {
-      Text("Koins")
-        .font(.system(size: 30, weight: .heavy))
-        .foregroundStyle(Theme.text)
-      Text("Monero and XRP wallet")
-        .font(.system(size: 13))
-        .foregroundStyle(Theme.muted)
+    HStack(alignment: .firstTextBaseline) {
+      VStack(alignment: .leading, spacing: 4) {
+        Text("Koins")
+          .font(.system(size: 30, weight: .heavy))
+          .foregroundStyle(Theme.text)
+        Text("Monero and XRP wallet")
+          .font(.system(size: 13))
+          .foregroundStyle(Theme.muted)
+      }
+      Spacer()
+      Button {
+        showSettings = true
+      } label: {
+        Image(systemName: "gearshape")
+          .font(.system(size: 17, weight: .medium))
+          .foregroundStyle(Theme.muted)
+          .frame(width: 36, height: 36)
+          .background(Theme.surface)
+          .clipShape(Circle())
+      }
     }
     .frame(maxWidth: .infinity, alignment: .leading)
   }
diff --git a/apps/ios/Koins/Views/SettingsView.swift b/apps/ios/Koins/Views/SettingsView.swift
new file mode 100644
index 0000000..0da3367
--- /dev/null
+++ b/apps/ios/Koins/Views/SettingsView.swift
@@ -0,0 +1,44 @@
+import SwiftUI
+
+struct SettingsView: View {
+  @EnvironmentObject private var model: AppModel
+  @Environment(\.dismiss) private var dismiss
+
+  var body: some View {
+    ZStack {
+      Theme.background.ignoresSafeArea()
+      VStack(alignment: .leading, spacing: 18) {
+        ScreenHeader(title: "Settings", subtitle: "Security and device options", onBack: { dismiss() })
+
+        Card {
+          Toggle(isOn: Binding(get: { model.faceIDEnabled },
+                               set: { model.faceIDEnabled = $0 })) {
+            VStack(alignment: .leading, spacing: 3) {
+              Text("Unlock with \(Biometrics.label)")
+                .font(.system(size: 15, weight: .semibold))
+                .foregroundStyle(Theme.text)
+              Text("Require \(Biometrics.label) to open the app, reveal the recovery phrase, and send payments.")
+                .font(.system(size: 11))
+                .foregroundStyle(Theme.muted)
+            }
+          }
+          .tint(Theme.accent)
+          .disabled(!Biometrics.isAvailable)
+
+          if !Biometrics.isAvailable {
+            Text("This device has no biometric sensor configured.")
+              .font(.system(size: 11))
+              .foregroundStyle(Theme.muted)
+          }
+        }
+
+        Spacer(minLength: 0)
+      }
+      .padding(.horizontal, 20)
+      .padding(.top, 12)
+    }
+    .preferredColorScheme(.dark)
+    .presentationDetents([.medium])
+    .presentationDragIndicator(.visible)
+  }
+}
\ No newline at end of file
diff --git a/apps/ios/project.yml b/apps/ios/project.yml
index 7e68967..3d7e7a7 100644
--- a/apps/ios/project.yml
+++ b/apps/ios/project.yml
@@ -67,6 +67,7 @@ targets:
           - UIInterfaceOrientationPortrait
         UIUserInterfaceStyle: Dark
         NSCameraUsageDescription: Scan a QR code to fill in a payment address.
+        NSFaceIDUsageDescription: Unlock Koins and approve payments.
         NSAppTransportSecurity:
           NSAllowsArbitraryLoads: true