diff --git a/js/scanner.js b/js/scanner.js
index 7274781..1462209 100644
--- a/js/scanner.js
+++ b/js/scanner.js
@@ -27,6 +27,7 @@
 	let currentProduct = null;
 	let selectedSupplier = null;
 	let allSuppliers = [];
+	let quaggaInitialized = false;
 
 	// DOM Elements (will be set on init)
 	let elements = {};
@@ -48,10 +49,54 @@
 			return;
 		}
 
+		// Check for camera support
+		checkCameraSupport();
+
 		bindEvents();
 		loadAllSuppliers();
 	}
 
+	// Check camera support and show appropriate messages
+	function checkCameraSupport() {
+		// Check HTTPS (required for camera access except on localhost)
+		// Note: In test environments without HTTPS, camera may not work but we still allow trying
+		const isSecure = location.protocol === 'https:' || location.hostname === 'localhost' || location.hostname === '127.0.0.1';
+
+		if (!isSecure) {
+			// Show warning but don't disable - some browsers/configs may still work
+			console.warn('HandyBarcodeScanner: HTTPS empfohlen für Kamerazugriff');
+		}
+
+		// Check if getUserMedia is supported
+		if (!navigator.mediaDevices || !navigator.mediaDevices.getUserMedia) {
+			showCameraError('Kamera wird von diesem Browser nicht unterstützt');
+			elements.startBtn.disabled = true;
+			elements.startBtn.classList.add('butActionRefused');
+			elements.startBtn.classList.remove('butAction');
+			return;
+		}
+
+		// Check if Quagga is loaded
+		if (typeof Quagga === 'undefined') {
+			showCameraError('Scanner-Bibliothek nicht geladen');
+			elements.startBtn.disabled = true;
+			elements.startBtn.classList.add('butActionRefused');
+			elements.startBtn.classList.remove('butAction');
+			return;
+		}
+
+		// All checks passed - enable button
+		elements.startBtn.disabled = false;
+	}
+
+	function showCameraError(message) {
+		const errorDiv = document.createElement('div');
+		errorDiv.className = 'error-message';
+		errorDiv.style.cssText = 'position: absolute; top: 50%; left: 50%; transform: translate(-50%, -50%); color: #fff; text-align: center; padding: 20px;';
+		errorDiv.innerHTML = '<div style="font-size: 40px; margin-bottom: 10px;">⚠️</div><div>' + message + '</div>';
+		elements.videoContainer.appendChild(errorDiv);
+	}
+
 	// Event Bindings
 	function bindEvents() {
 		elements.startBtn.addEventListener('click', startScanner);
@@ -73,6 +118,7 @@
 	// Scanner Functions
 	function startScanner() {
 		if (isScanning) return;
+		if (elements.startBtn.disabled) return;
 
 		// Check if Quagga is available
 		if (typeof Quagga === 'undefined') {
@@ -80,6 +126,10 @@
 			return;
 		}
 
+		// Disable button while initializing
+		elements.startBtn.disabled = true;
+		elements.startBtn.textContent = 'Initialisiere...';
+
 		Quagga.init({
 			inputStream: {
 				name: "Live",
@@ -87,8 +137,8 @@
 				target: elements.videoContainer,
 				constraints: {
 					facingMode: "environment",
-					width: { ideal: 1280 },
-					height: { ideal: 720 }
+					width: { min: 640, ideal: 1280, max: 1920 },
+					height: { min: 480, ideal: 720, max: 1080 }
 				}
 			},
 			decoder: {
@@ -104,25 +154,48 @@
 		}, function(err) {
 			if (err) {
 				console.error('Quagga init error:', err);
-				showToast(CONFIG.lang.cameraError, 'error');
+				elements.startBtn.disabled = false;
+				elements.startBtn.textContent = CONFIG.lang.startScan || 'Scan starten';
+
+				// Show specific error message
+				let errorMsg = CONFIG.lang.cameraError || 'Kamerafehler';
+				if (err.name === 'NotAllowedError') {
+					errorMsg = 'Kamerazugriff verweigert. Bitte Berechtigung erteilen.';
+				} else if (err.name === 'NotFoundError') {
+					errorMsg = 'Keine Kamera gefunden.';
+				} else if (err.name === 'NotReadableError') {
+					errorMsg = 'Kamera wird bereits verwendet.';
+				}
+				showToast(errorMsg, 'error');
 				return;
 			}
+
+			// Success - start scanning
 			Quagga.start();
+			quaggaInitialized = true;
 			isScanning = true;
 			elements.startBtn.classList.add('hidden');
 			elements.stopBtn.classList.remove('hidden');
 			elements.videoContainer.classList.add('scanning');
-		});
 
-		Quagga.onDetected(onBarcodeDetected);
+			// Register detection handler
+			Quagga.onDetected(onBarcodeDetected);
+		});
 	}
 
 	function stopScanner() {
 		if (!isScanning) return;
 
-		Quagga.stop();
+		if (quaggaInitialized) {
+			Quagga.offDetected(onBarcodeDetected);
+			Quagga.stop();
+		}
+
 		isScanning = false;
+		quaggaInitialized = false;
 		elements.startBtn.classList.remove('hidden');
+		elements.startBtn.disabled = false;
+		elements.startBtn.textContent = CONFIG.lang.startScan || 'Scan starten';
 		elements.stopBtn.classList.add('hidden');
 		elements.videoContainer.classList.remove('scanning');
 	}