diff --git a/README.md b/README.md
index 754cb27..eb62bff 100644
--- a/README.md
+++ b/README.md
@@ -18,7 +18,8 @@ no SSH client and no external terminal needed.
 - **Shell picker** — run zsh, bash, fish, PowerShell… whatever the machine actually has
 - **Mobile key bar** — Esc, Tab, Ctrl, Alt, `^C`/`^D`/`^Z`, arrows, Home/End/PgUp/PgDn and the
   punctuation soft keyboards hide. The Ctrl and Alt keys apply to the next character you type,
-  so `Ctrl+<anything>` works from a phone.
+  so `Ctrl+<anything>` works from a phone; double-tap one to lock it for repeated chords (such as
+  a double `Ctrl+C`) until it is tapped again.
 - **Undo close** — closing a tab is recoverable for 8 seconds before the shell is killed
 - **Offline-ready** — xterm.js is bundled into the plugin, not fetched from a CDN at runtime
 - **Accessible** — keyboard-operable tabs and settings, ARIA labels, optional screen-reader mode,
diff --git a/src/index.ts b/src/index.ts
index c80de11..8c6a49b 100644
--- a/src/index.ts
+++ b/src/index.ts
@@ -117,8 +117,8 @@ const MOBILE_KEYS: KeyDef[] = [
   { label: IC.paste, svg: true, action: 'paste', title: 'Paste' },
   { label: 'ESC', seq: '\x1b' },
   { label: 'TAB', seq: '\t' },
-  { label: 'CTRL', action: 'ctrl', title: 'Ctrl — applies to the next key you type' },
-  { label: 'ALT', action: 'alt', title: 'Alt — applies to the next key you type' },
+  { label: 'CTRL', action: 'ctrl', title: 'Ctrl — applies to the next key you type; double-tap to lock' },
+  { label: 'ALT', action: 'alt', title: 'Alt — applies to the next key you type; double-tap to lock' },
   // Ctrl+C used to be impossible from a phone: the bar had a CTRL toggle but
   // no letters for it to combine with.
   { label: '^C', seq: '\x03', title: 'Ctrl+C (interrupt)' },
@@ -627,7 +627,9 @@ export async function mount(container: HTMLElement, api: PluginAPI): Promise<voi
     const session = activeSession();
     for (const { action, button } of modifierButtons) {
       const armed = action === 'ctrl' ? session?.pendingCtrl : session?.pendingAlt;
+      const locked = action === 'ctrl' ? session?.ctrlLocked : session?.altLocked;
       button.classList.toggle('wt-active', !!armed);
+      button.classList.toggle('wt-locked', !!locked);
       button.setAttribute('aria-pressed', String(!!armed));
     }
   }
@@ -648,13 +650,13 @@ export async function mount(container: HTMLElement, api: PluginAPI): Promise<voi
     }
 
     if (key.action === 'ctrl' || key.action === 'alt') {
-      modifierButtons.push({ action: key.action, button });
+      const modifier = key.action;
+      modifierButtons.push({ action: modifier, button });
       button.setAttribute('aria-pressed', 'false');
       button.addEventListener('click', () => {
         const session = activeSession();
         if (!session) return;
-        if (key.action === 'ctrl') session.pendingCtrl = !session.pendingCtrl;
-        else session.pendingAlt = !session.pendingAlt;
+        session.tapModifier(modifier);
         syncModifierButtons();
         session.focus();
       });
diff --git a/src/session.ts b/src/session.ts
index 89b236b..0c51b54 100644
--- a/src/session.ts
+++ b/src/session.ts
@@ -25,6 +25,8 @@ export type SessionStatus = 'connecting' | 'connected' | 'reconnecting' | 'disco
 const CONNECT_TIMEOUT_MS = 12000;
 const MAX_RECONNECT_DELAY_MS = 15000;
 const PING_INTERVAL_MS = 25000;
+/** Two taps on a key bar modifier within this window lock it. */
+const DOUBLE_TAP_MS = 500;
 
 const encoder = new TextEncoder();
 
@@ -78,6 +80,9 @@ export class TerminalSession {
   /** Set while a modifier key from the mobile bar is armed for the next press. */
   pendingCtrl = false;
   pendingAlt = false;
+  /** A locked modifier stays armed after each key until it is tapped again. */
+  ctrlLocked = false;
+  altLocked = false;
   onModifiersChange: (() => void) | null = null;
 
   private readonly overlayEl: HTMLElement;
@@ -106,6 +111,7 @@ export class TerminalSession {
   private pendingResume: string | null;
   /** Set while restart() is in flight, so the fresh shell is not reported as an expiry. */
   private restarting = false;
+  private modifierTapAt = { ctrl: 0, alt: 0 };
 
   private readonly onOnline = (): void => { if (this.status === 'reconnecting') this.connect(true); };
   private readonly onVisible = (): void => {
@@ -369,6 +375,24 @@ export class TerminalSession {
     }
   }
 
+  /**
+   * A tap on CTRL or ALT in the key bar. A single tap arms the modifier for
+   * the next key, as before; a second tap right after locks it, so a chord
+   * that repeats — Claude Code's double Ctrl+C to exit — can be typed at all.
+   * Any tap on a locked modifier releases it.
+   */
+  tapModifier(which: 'ctrl' | 'alt'): void {
+    const now = performance.now();
+    const armed = which === 'ctrl' ? this.pendingCtrl : this.pendingAlt;
+    const locked = which === 'ctrl' ? this.ctrlLocked : this.altLocked;
+    const doubleTap = armed && !locked && now - this.modifierTapAt[which] < DOUBLE_TAP_MS;
+    const nextLocked = doubleTap;
+    const nextArmed = doubleTap || (!armed && !locked);
+    this.modifierTapAt[which] = nextArmed && !nextLocked ? now : 0;
+    if (which === 'ctrl') { this.pendingCtrl = nextArmed; this.ctrlLocked = nextLocked; }
+    else { this.pendingAlt = nextArmed; this.altLocked = nextLocked; }
+  }
+
   private handleInput(data: string): void {
     // A modifier armed from the on-screen key bar applies to the next
     // character the soft keyboard produces, which is the only way to type
@@ -381,8 +405,8 @@ export class TerminalSession {
         else if (code >= 64 && code <= 95) out = String.fromCharCode(code - 64);
       }
       if (this.pendingAlt) out = `\x1b${out}`;
-      this.pendingCtrl = false;
-      this.pendingAlt = false;
+      if (!this.ctrlLocked) this.pendingCtrl = false;
+      if (!this.altLocked) this.pendingAlt = false;
       this.onModifiersChange?.();
       this.sendBytes(encoder.encode(out));
       return;
diff --git a/src/ui/styles.ts b/src/ui/styles.ts
index 9e9c883..62a15f5 100644
--- a/src/ui/styles.ts
+++ b/src/ui/styles.ts
@@ -171,6 +171,7 @@ const PLUGIN_CSS = `
   user-select:none; -webkit-tap-highlight-color:transparent;
 }
 .wt-key:active, .wt-key.wt-active { background:var(--accent); color:#fff; border-color:var(--accent); }
+.wt-key.wt-locked { box-shadow:inset 0 0 0 2px rgba(255,255,255,.85); }
 .wt-key, .wt-btn, .wt-tab, .wt-tab-close, .wt-new-tab { touch-action:manipulation; }
 .wt-key svg { width:16px; height:16px; }