diff --git a/webui/web/css/main.css b/webui/web/css/main.css
index 4c5d0ab..1e2627c 100644
--- a/webui/web/css/main.css
+++ b/webui/web/css/main.css
@@ -1093,6 +1093,70 @@ body {
     display: none;
 }
 
+/* ===== MODAL ===== */
+.modal-overlay {
+    position: fixed;
+    inset: 0;
+    background: rgba(0, 0, 0, 0.7);
+    backdrop-filter: blur(4px);
+    display: flex;
+    align-items: center;
+    justify-content: center;
+    z-index: 1001;
+    opacity: 0;
+    transition: opacity var(--transition-base);
+    padding: var(--space-4);
+}
+
+.modal-overlay.show {
+    opacity: 1;
+}
+
+.modal-overlay.hidden {
+    display: none;
+}
+
+.modal {
+    background: var(--bg-elevated);
+    border: 1px solid var(--border-color);
+    border-radius: 12px;
+    padding: var(--space-8);
+    max-width: 400px;
+    width: 100%;
+    box-shadow: var(--shadow-lg);
+    transform: scale(0.95);
+    transition: transform var(--transition-base);
+    text-align: center;
+}
+
+.modal-overlay.show .modal {
+    transform: scale(1);
+}
+
+.modal-title {
+    font-size: var(--text-xl);
+    font-weight: 700;
+    color: var(--error);
+    margin-bottom: var(--space-4);
+}
+
+.modal-message {
+    font-size: var(--text-base);
+    color: var(--text-secondary);
+    margin-bottom: var(--space-8);
+    line-height: 1.6;
+}
+
+.modal-actions {
+    display: flex;
+    gap: var(--space-3);
+}
+
+.modal-actions .btn {
+    flex: 1;
+    padding: var(--space-4);
+}
+
 /* ===== ANIMATIONS ===== */
 @keyframes fadeIn {
     from {
diff --git a/webui/web/index.html b/webui/web/index.html
index 21d573d..53ae618 100644
--- a/webui/web/index.html
+++ b/webui/web/index.html
@@ -643,6 +643,9 @@
         </div>
     </div>
 
+    <!-- Modal -->
+    <div id="modal-overlay" class="modal-overlay hidden"></div>
+
     <!-- Toast Notification -->
     <div id="toast" class="toast hidden"></div>
 
diff --git a/webui/web/js/api/probe.js b/webui/web/js/api/probe.js
new file mode 100644
index 0000000..dc72129
--- /dev/null
+++ b/webui/web/js/api/probe.js
@@ -0,0 +1,24 @@
+export class ProbeAPI {
+    constructor(baseURL = '') {
+        this.baseURL = baseURL;
+    }
+
+    /**
+     * Probe a device at the given IP address.
+     * Returns device info: reachable status, vendor, hostname, mDNS data.
+     * @param {string} ip - IP address to probe
+     * @returns {Promise<Object>} Probe response
+     */
+    async probe(ip) {
+        const response = await fetch(
+            `${this.baseURL}api/v1/probe?ip=${encodeURIComponent(ip)}`
+        );
+
+        if (!response.ok) {
+            const text = await response.text();
+            throw new Error(text || `HTTP ${response.status}`);
+        }
+
+        return await response.json();
+    }
+}
diff --git a/webui/web/js/main.js b/webui/web/js/main.js
index fa2fccf..14978c8 100644
--- a/webui/web/js/main.js
+++ b/webui/web/js/main.js
@@ -1,5 +1,6 @@
 import { CameraSearchAPI } from './api/camera-search.js';
 import { StreamDiscoveryAPI } from './api/stream-discovery.js';
+import { ProbeAPI } from './api/probe.js';
 import { MockCameraAPI } from './mock/mock-camera-api.js';
 import { MockStreamAPI } from './mock/mock-stream-api.js';
 import { SearchForm } from './ui/search-form.js';
@@ -7,6 +8,7 @@ import { StreamList } from './ui/stream-list.js';
 import { ConfigPanel } from './ui/config-panel.js';
 import { FrigateGenerator } from './config-generators/frigate/index.js';
 import { showToast } from './utils/toast.js';
+import { showModal } from './ui/modal.js';
 
 class StrixApp {
     constructor() {
@@ -29,6 +31,9 @@ class StrixApp {
             this.streamAPI = new StreamDiscoveryAPI();
         }
 
+        this.probeAPI = new ProbeAPI();
+        this.probeResult = null;
+
         this.searchForm = new SearchForm();
         this.streamList = new StreamList();
         this.configPanel = new ConfigPanel();
@@ -170,7 +175,88 @@ class StrixApp {
             document.getElementById('address-validated').value = address;
         }
 
-        this.showScreen('config');
+        // Extract IP for probe (from full URL or raw input)
+        const probeIP = this.extractIPForProbe(address);
+
+        // Probe the device before proceeding
+        const btn = document.getElementById('btn-check-address');
+        const originalText = btn.textContent;
+        btn.disabled = true;
+        btn.textContent = 'Checking...';
+
+        try {
+            this.probeResult = await this.probeAPI.probe(probeIP);
+
+            if (this.probeResult.reachable) {
+                // Auto-fill vendor into Camera Model if found
+                if (this.probeResult.probes.arp && this.probeResult.probes.arp.vendor) {
+                    const modelInput = document.getElementById('camera-model');
+                    if (!modelInput.disabled && !modelInput.value) {
+                        modelInput.value = this.probeResult.probes.arp.vendor;
+                    }
+                }
+
+                this.showScreen('config');
+            } else {
+                // Device unreachable -- show modal
+                const result = await showModal({
+                    title: 'Device Unreachable',
+                    message: `The device at ${probeIP} is not responding. It may be offline, on a different network, or the IP address may be incorrect.`,
+                    buttons: [
+                        { id: 'change', label: 'Change IP', style: 'primary' },
+                        { id: 'continue', label: 'Continue Anyway', style: 'outline' }
+                    ]
+                });
+
+                if (result === 'continue') {
+                    this.showScreen('config');
+                } else {
+                    // 'change' or null (overlay click) -- stay on address screen
+                    input.focus();
+                    input.select();
+                }
+            }
+        } catch (error) {
+            // Network/server error -- show modal
+            const result = await showModal({
+                title: 'Connection Error',
+                message: `Could not check the device: ${error.message}`,
+                buttons: [
+                    { id: 'change', label: 'Change IP', style: 'primary' },
+                    { id: 'continue', label: 'Continue Anyway', style: 'outline' }
+                ]
+            });
+
+            if (result === 'continue') {
+                this.showScreen('config');
+            } else {
+                input.focus();
+            }
+        } finally {
+            btn.disabled = false;
+            btn.textContent = originalText;
+        }
+    }
+
+    /**
+     * Extract IP address from input for probe API call.
+     * Handles plain IPs and full URLs like rtsp://user:pass@192.168.1.50/stream
+     */
+    extractIPForProbe(address) {
+        if (this.isFullURL(address)) {
+            try {
+                const urlObj = new URL(address);
+                return urlObj.hostname;
+            } catch (e) {
+                return address;
+            }
+        }
+        // Remove port if present (e.g., "192.168.1.50:554")
+        const colonIndex = address.lastIndexOf(':');
+        if (colonIndex > 0) {
+            return address.substring(0, colonIndex);
+        }
+        return address;
     }
 
     isFullURL(str) {
diff --git a/webui/web/js/ui/modal.js b/webui/web/js/ui/modal.js
new file mode 100644
index 0000000..96f0693
--- /dev/null
+++ b/webui/web/js/ui/modal.js
@@ -0,0 +1,83 @@
+/**
+ * Simple modal dialog component.
+ * Shows a centered card with title, message, and configurable buttons.
+ * Returns a Promise that resolves with the clicked button's id.
+ *
+ * Usage:
+ *   const result = await showModal({
+ *       title: 'Device Unreachable',
+ *       message: 'This IP is not responding.',
+ *       buttons: [
+ *           { id: 'change', label: 'Change IP', style: 'primary' },
+ *           { id: 'continue', label: 'Continue Anyway', style: 'outline' }
+ *       ]
+ *   });
+ */
+
+let currentResolve = null;
+
+export function showModal({ title, message, buttons }) {
+    return new Promise((resolve) => {
+        currentResolve = resolve;
+
+        const overlay = document.getElementById('modal-overlay');
+
+        // Clear previous content safely
+        overlay.replaceChildren();
+
+        // Build modal DOM using safe DOM methods
+        const modal = document.createElement('div');
+        modal.className = 'modal';
+
+        const titleEl = document.createElement('div');
+        titleEl.className = 'modal-title';
+        titleEl.textContent = title;
+        modal.appendChild(titleEl);
+
+        const messageEl = document.createElement('div');
+        messageEl.className = 'modal-message';
+        messageEl.textContent = message;
+        modal.appendChild(messageEl);
+
+        const actionsEl = document.createElement('div');
+        actionsEl.className = 'modal-actions';
+
+        buttons.forEach(btnConfig => {
+            const btn = document.createElement('button');
+            btn.className = `btn btn-${btnConfig.style || 'outline'}`;
+            btn.textContent = btnConfig.label;
+            btn.addEventListener('click', () => {
+                hideModal();
+                resolve(btnConfig.id);
+            });
+            actionsEl.appendChild(btn);
+        });
+
+        modal.appendChild(actionsEl);
+        overlay.appendChild(modal);
+
+        // Close on overlay click (outside modal)
+        overlay.addEventListener('click', (e) => {
+            if (e.target === overlay) {
+                hideModal();
+                resolve(null);
+            }
+        });
+
+        // Show with animation
+        overlay.classList.remove('hidden');
+        requestAnimationFrame(() => {
+            overlay.classList.add('show');
+        });
+    });
+}
+
+export function hideModal() {
+    const overlay = document.getElementById('modal-overlay');
+    overlay.classList.remove('show');
+    setTimeout(() => {
+        overlay.classList.add('hidden');
+        overlay.replaceChildren();
+    }, 200);
+    currentResolve = null;
+}