diff --git a/intercept_agent.py b/intercept_agent.py
index beabeaf..381c82f 100644
--- a/intercept_agent.py
+++ b/intercept_agent.py
@@ -2357,6 +2357,37 @@ class ModeManager:
     # ACARS MODE (acarsdec)
     # -------------------------------------------------------------------------
 
+    def _detect_acarsdec_fork(self, acarsdec_path: str) -> str:
+        """Detect which acarsdec fork is installed.
+
+        Returns:
+            '--output' for f00b4r0 fork (DragonOS)
+            '-j' for TLeconte v4+
+            '-o' for TLeconte v3.x
+        """
+        try:
+            result = subprocess.run(
+                [acarsdec_path],
+                capture_output=True,
+                text=True,
+                timeout=5
+            )
+            output = result.stdout + result.stderr
+
+            # f00b4r0 fork uses --output instead of -j/-o
+            if '--output' in output:
+                return '--output'
+
+            # Parse version for TLeconte
+            import re
+            version_match = re.search(r'acarsdec[^\d]*v?(\d+)\.(\d+)', output, re.IGNORECASE)
+            if version_match:
+                major = int(version_match.group(1))
+                return '-j' if major >= 4 else '-o'
+        except Exception:
+            pass
+        return '-j'  # Default to TLeconte v4+
+
     def _start_acars(self, params: dict) -> dict:
         """Start ACARS decoding using acarsdec."""
         gain = params.get('gain', '40')
@@ -2367,10 +2398,24 @@ class ModeManager:
         if not acarsdec_path:
             return {'status': 'error', 'message': 'acarsdec not found. Install acarsdec.'}
 
-        # Build command with JSON output
-        cmd = [acarsdec_path, '-j', '-r', str(device), '-g', str(gain)]
-        for freq in frequencies:
-            cmd.append(freq)
+        # Detect fork and build appropriate command
+        fork_type = self._detect_acarsdec_fork(acarsdec_path)
+        cmd = [acarsdec_path]
+
+        if fork_type == '--output':
+            # f00b4r0 fork (DragonOS): different syntax
+            cmd.extend(['--output', 'json:file'])  # stdout
+            cmd.extend(['-g', str(gain)])
+            cmd.extend(['-m', '256'])  # 3.2 MS/s for wider bandwidth
+            cmd.extend(['--rtlsdr', str(device)])
+        elif fork_type == '-j':
+            # TLeconte v4+
+            cmd.extend(['-j', '-g', str(gain), '-r', str(device)])
+        else:
+            # TLeconte v3.x
+            cmd.extend(['-o', '4', '-g', str(gain), '-r', str(device)])
+
+        cmd.extend(frequencies)
 
         logger.info(f"Starting acarsdec: {' '.join(cmd)}")
 
diff --git a/static/js/core/agents.js b/static/js/core/agents.js
index 5c073aa..c29779f 100644
--- a/static/js/core/agents.js
+++ b/static/js/core/agents.js
@@ -678,7 +678,8 @@ function syncModeUI(mode, isRunning, agentId = null) {
         'pager': 'setPagerRunning',
         'adsb': 'setADSBRunning',
         'wifi': 'setWiFiRunning',
-        'bluetooth': 'setBluetoothRunning'
+        'bluetooth': 'setBluetoothRunning',
+        'acars': 'setAcarsRunning'
     };
 
     const setterName = uiSetters[mode];
diff --git a/templates/adsb_dashboard.html b/templates/adsb_dashboard.html
index 4a4b77b..119f6b2 100644
--- a/templates/adsb_dashboard.html
+++ b/templates/adsb_dashboard.html
@@ -3763,6 +3763,30 @@ sudo make install</code>
                 });
         }
 
+        // Sync ACARS UI state (called by syncModeUI in agents.js)
+        function setAcarsRunning(running, agentId = null) {
+            isAcarsRunning = running;
+            const btn = document.getElementById('acarsToggleBtn');
+            const indicator = document.getElementById('acarsPanelIndicator');
+
+            if (running) {
+                acarsCurrentAgent = agentId;
+                btn.textContent = '■ STOP ACARS';
+                btn.classList.add('active');
+                if (indicator) indicator.classList.add('active');
+                // Start stream if not already running
+                if (!acarsEventSource && !acarsPollTimer) {
+                    startAcarsStream(agentId !== null);
+                }
+            } else {
+                btn.textContent = '▶ START ACARS';
+                btn.classList.remove('active');
+                if (indicator) indicator.classList.remove('active');
+            }
+        }
+        // Expose to global scope for syncModeUI
+        window.setAcarsRunning = setAcarsRunning;
+
         function startAcarsStream(isAgentMode = false) {
             if (acarsEventSource) acarsEventSource.close();