diff --git a/src/DeviceManager.ts b/src/DeviceManager.ts
new file mode 100644
index 0000000..4d25242
--- /dev/null
+++ b/src/DeviceManager.ts
@@ -0,0 +1,180 @@
+"use strict";
+
+import { Platform } from "obsidian";
+import type { LoginManager } from "./LoginManager";
+import { Observable } from "./observable/Observable";
+
+const DEVICE_ID_KEY = "relay-device-id";
+
+/**
+ * Generate a PocketBase-compatible ID.
+ * Format: 15 characters, lowercase alphanumeric only.
+ */
+function generatePocketBaseId(): string {
+	const chars = "abcdefghijklmnopqrstuvwxyz0123456789";
+	const array = new Uint8Array(15);
+	crypto.getRandomValues(array);
+	return Array.from(array, (byte) => chars[byte % chars.length]).join("");
+}
+
+/**
+ * Get platform string for device registration.
+ */
+function getPlatform(): string {
+	if (Platform.isIosApp) return "Phone (iOS)";
+	if (Platform.isAndroidApp) return "Phone (Android)";
+	if (Platform.isMacOS) return "Desktop (macOS)";
+	if (Platform.isWin) return "Desktop (Windows)";
+	if (Platform.isLinux) return "Desktop (Linux)";
+	if (Platform.isMobile) return "Mobile";
+	return "Desktop";
+}
+
+export class DeviceManager extends Observable<DeviceManager> {
+	private deviceId: string | null = null;
+	private registered = false;
+
+	constructor(
+		private appId: string,
+		private vaultName: string,
+		private loginManager: LoginManager,
+	) {
+		super("DeviceManager");
+	}
+
+	/**
+	 * Get or create the device ID from localStorage.
+	 */
+	getDeviceId(): string {
+		if (this.deviceId) return this.deviceId;
+
+		let id = localStorage.getItem(DEVICE_ID_KEY);
+		if (!id) {
+			id = generatePocketBaseId();
+			localStorage.setItem(DEVICE_ID_KEY, id);
+			this.log("Generated new device ID:", id);
+		}
+		this.deviceId = id;
+		return id;
+	}
+
+	/**
+	 * Get platform string.
+	 */
+	getPlatform(): string {
+		return getPlatform();
+	}
+
+	/**
+	 * Register device and vault with PocketBase.
+	 * Creates records if they don't exist, updates if they do.
+	 */
+	async register(): Promise<void> {
+		if (this.registered) {
+			this.debug("Already registered this session");
+			return;
+		}
+
+		if (!this.loginManager.loggedIn) {
+			this.debug("Not logged in, skipping registration");
+			return;
+		}
+
+		const deviceId = this.getDeviceId();
+		const platform = this.getPlatform();
+		const userId = this.loginManager.user?.id;
+
+		if (!userId) {
+			this.warn("No user ID available");
+			return;
+		}
+
+		try {
+			// Register device
+			await this.registerDevice(deviceId, platform, userId);
+
+			// Register vault
+			await this.registerVault(this.appId, this.vaultName, deviceId, userId);
+
+			this.registered = true;
+			this.log("Device and vault registered successfully");
+		} catch (error) {
+			this.error("Failed to register device/vault:", error);
+		}
+	}
+
+	private async registerDevice(
+		deviceId: string,
+		platform: string,
+		userId: string,
+	): Promise<void> {
+		const pb = this.loginManager.pb;
+
+		try {
+			// Try to create new device record
+			await pb.collection("devices").create({
+				id: deviceId,
+				name: platform,
+				platform: platform,
+				user: userId,
+			});
+			this.log("Created new device record:", deviceId);
+		} catch (e: any) {
+			// Record may already exist, try to update
+			if (e.status === 400 || e.status === 409) {
+				try {
+					await pb.collection("devices").update(deviceId, {
+						platform: platform,
+						user: userId,
+					});
+					this.log("Updated existing device record:", deviceId);
+				} catch (updateError) {
+					this.error("Failed to update device:", updateError);
+					throw updateError;
+				}
+			} else {
+				throw e;
+			}
+		}
+	}
+
+	private async registerVault(
+		vaultId: string,
+		vaultName: string,
+		deviceId: string,
+		userId: string,
+	): Promise<void> {
+		const pb = this.loginManager.pb;
+
+		try {
+			// Try to create new vault record
+			await pb.collection("vaults").create({
+				id: vaultId,
+				name: vaultName,
+				device: deviceId,
+				user: userId,
+			});
+			this.log("Created new vault record:", vaultId);
+		} catch (e: any) {
+			// Record may already exist, try to update
+			if (e.status === 400 || e.status === 409) {
+				try {
+					await pb.collection("vaults").update(vaultId, {
+						name: vaultName,
+						device: deviceId,
+					});
+					this.log("Updated existing vault record:", vaultId);
+				} catch (updateError) {
+					this.error("Failed to update vault:", updateError);
+					throw updateError;
+				}
+			} else {
+				throw e;
+			}
+		}
+	}
+
+	override destroy(): void {
+		super.destroy();
+	}
+}
diff --git a/src/LoginManager.ts b/src/LoginManager.ts
index 6b4e583..c7b9492 100644
--- a/src/LoginManager.ts
+++ b/src/LoginManager.ts
@@ -1,6 +1,6 @@
 "use strict";
 
-import { requestUrl, type RequestUrlResponsePromise } from "obsidian";
+import { apiVersion, requestUrl, type RequestUrlResponsePromise } from "obsidian";
 import { User } from "./User";
 import PocketBase, {
 	BaseAuthStore,
@@ -13,7 +13,7 @@ import { Observable } from "./observable/Observable";
 
 declare const GIT_TAG: string;
 
-import { customFetch } from "./customFetch";
+import { customFetch, getDeviceManagementHeaders } from "./customFetch";
 import { LocalAuthStore } from "./pocketbase/LocalAuthStore";
 import type { TimeProvider } from "./TimeProvider";
 import { FeatureFlagManager } from "./flagManager";
@@ -192,6 +192,7 @@ export class LoginManager extends Observable<LoginManager> {
 			options.fetch = customFetch;
 			options.headers = Object.assign({}, options.headers, {
 				"Relay-Version": GIT_TAG,
+				"Obsidian-Version": apiVersion,
 			});
 			return { url, options };
 		};
@@ -283,6 +284,8 @@ export class LoginManager extends Observable<LoginManager> {
 		const headers = {
 			Authorization: `Bearer ${this.pb.authStore.token}`,
 			"Relay-Version": GIT_TAG,
+			"Obsidian-Version": apiVersion,
+			...getDeviceManagementHeaders(),
 		};
 		return requestUrl({
 			url: `${this.endpointManager.getApiUrl()}/relay/${relay_guid}/check-host`,
@@ -295,6 +298,8 @@ export class LoginManager extends Observable<LoginManager> {
 		const headers = {
 			Authorization: `Bearer ${this.pb.authStore.token}`,
 			"Relay-Version": GIT_TAG,
+			"Obsidian-Version": apiVersion,
+			...getDeviceManagementHeaders(),
 		};
 		requestUrl({
 			url: `${this.endpointManager.getApiUrl()}/flags`,
@@ -315,6 +320,7 @@ export class LoginManager extends Observable<LoginManager> {
 	whoami() {
 		const headers = {
 			Authorization: `Bearer ${this.pb.authStore.token}`,
+			...getDeviceManagementHeaders(),
 		};
 		requestUrl({
 			url: `${this.endpointManager.getApiUrl()}/whoami`,
@@ -362,6 +368,7 @@ export class LoginManager extends Observable<LoginManager> {
 				options.fetch = customFetch;
 				options.headers = Object.assign({}, options.headers, {
 					"Relay-Version": GIT_TAG,
+					"Obsidian-Version": apiVersion,
 				});
 				return { url, options };
 			};
diff --git a/src/NetworkStatus.ts b/src/NetworkStatus.ts
index 36fdd60..090c1a3 100644
--- a/src/NetworkStatus.ts
+++ b/src/NetworkStatus.ts
@@ -1,6 +1,7 @@
-import { requestUrl } from "obsidian";
+import { apiVersion, requestUrl } from "obsidian";
 import { curryLog } from "./debug";
 import type { TimeProvider } from "./TimeProvider";
+import { getDeviceManagementHeaders } from "./customFetch";
 
 declare const GIT_TAG: string;
 
@@ -77,7 +78,11 @@ class NetworkStatus {
 		return requestUrl({
 			url: this.url,
 			method: "GET",
-			headers: { "Relay-Version": GIT_TAG },
+			headers: {
+				"Relay-Version": GIT_TAG,
+				"Obsidian-Version": apiVersion,
+				...getDeviceManagementHeaders(),
+			},
 		})
 			.then((response) => {
 				if (response.status === 200) {
diff --git a/src/customFetch.ts b/src/customFetch.ts
index 2ca8d56..6da0810 100644
--- a/src/customFetch.ts
+++ b/src/customFetch.ts
@@ -1,5 +1,5 @@
 "use strict";
-import { requestUrl } from "obsidian";
+import { apiVersion, requestUrl } from "obsidian";
 import { Platform } from "obsidian";
 import type { RequestUrlParam, RequestUrlResponse } from "obsidian";
 import { curryLog } from "./debug";
@@ -7,6 +7,37 @@ import { flags } from "./flagManager";
 
 declare const GIT_TAG: string;
 
+// Device management configuration
+let deviceManagementConfig: {
+	vaultId: string;
+	deviceId: string;
+} | null = null;
+
+/**
+ * Set device management configuration for headers.
+ * Called from main.ts after DeviceManager is initialized.
+ */
+export function setDeviceManagementConfig(config: {
+	vaultId: string;
+	deviceId: string;
+}): void {
+	deviceManagementConfig = config;
+}
+
+/**
+ * Get device management headers if enabled.
+ * Returns empty object if not enabled or not configured.
+ */
+export function getDeviceManagementHeaders(): Record<string, string> {
+	if (flags().enableDeviceManagement && deviceManagementConfig) {
+		return {
+			"Device-Id": deviceManagementConfig.deviceId,
+			"Vault-Id": deviceManagementConfig.vaultId,
+		};
+	}
+	return {};
+}
+
 if (globalThis.Response === undefined || globalThis.Headers === undefined) {
 	// Fetch API is broken for some versions of Electron
 	// https://github.com/electron/electron/pull/42419
@@ -47,9 +78,22 @@ export const customFetch = async (
 
 	const method = config?.method || "GET";
 
-	const headers = Object.assign({}, config?.headers, {
+	const baseHeaders: Record<string, string> = {
 		"Relay-Version": GIT_TAG,
-	}) as Record<string, string>;
+		"Obsidian-Version": apiVersion,
+	};
+
+	// Add device management headers if enabled
+	if (flags().enableDeviceManagement && deviceManagementConfig) {
+		baseHeaders["Device-Id"] = deviceManagementConfig.deviceId;
+		baseHeaders["Vault-Id"] = deviceManagementConfig.vaultId;
+	}
+
+	const headers = Object.assign(
+		{},
+		config?.headers,
+		baseHeaders,
+	) as Record<string, string>;
 
 	// Prepare the request parameters
 	const requestParams: RequestUrlParam = {
diff --git a/src/flags.ts b/src/flags.ts
index 2976c4f..9c47967 100644
--- a/src/flags.ts
+++ b/src/flags.ts
@@ -16,6 +16,7 @@ export interface FeatureFlags {
 	enablePreviewViewHooks: boolean;
 	enableMetadataViewHooks: boolean;
 	enableKanbanView: boolean;
+	enableDeviceManagement: boolean;
 }
 
 export const FeatureFlagDefaults: FeatureFlags = {
@@ -36,6 +37,7 @@ export const FeatureFlagDefaults: FeatureFlags = {
 	enablePreviewViewHooks: true,
 	enableMetadataViewHooks: true,
 	enableKanbanView: true,
+	enableDeviceManagement: false,
 } as const;
 
 export function isKeyOfFeatureFlags(key: string): key is keyof FeatureFlags {
diff --git a/src/main.ts b/src/main.ts
index 386ac66..dc6776a 100644
--- a/src/main.ts
+++ b/src/main.ts
@@ -63,6 +63,8 @@ import { ContentAddressedFileStore, isSyncFile } from "./SyncFile";
 import { isDocument } from "./Document";
 import { EndpointManager, type EndpointSettings } from "./EndpointManager";
 import { SelfHostModal } from "./ui/SelfHostModal";
+import { DeviceManager } from "./DeviceManager";
+import { setDeviceManagementConfig } from "./customFetch";
 
 interface DebugSettings {
 	debugging: boolean;
@@ -109,6 +111,7 @@ export default class Live extends Plugin {
 	backgroundSync!: BackgroundSync;
 	folderNavDecorations!: FolderNavigationDecorations;
 	relayManager!: RelayManager;
+	deviceManager!: DeviceManager;
 	settingsTab!: LiveSettingsTab;
 	settings!: Settings<RelaySettings>;
 	updateManager!: UpdateManager;
@@ -529,6 +532,15 @@ export default class Live extends Plugin {
 			endpointManager,
 		);
 		this.relayManager = new RelayManager(this.loginManager);
+		this.deviceManager = new DeviceManager(
+			this.appId,
+			this.vault.getName(),
+			this.loginManager,
+		);
+		setDeviceManagementConfig({
+			vaultId: this.appId,
+			deviceId: this.deviceManager.getDeviceId(),
+		});
 		this.sharedFolders = new SharedFolders(
 			this.relayManager,
 			this.vault,
@@ -771,6 +783,9 @@ export default class Live extends Plugin {
 		this.sharedFolders.load();
 		this.relayManager?.login();
 		this._liveViews.refresh("login");
+		withFlag(flag.enableDeviceManagement, () => {
+			this.deviceManager.register();
+		});
 	}
 
 	async openSettings(path: string = "/") {
@@ -1167,6 +1182,9 @@ export default class Live extends Plugin {
 		this.relayManager?.destroy();
 		this.relayManager = null as any;
 
+		this.deviceManager?.destroy();
+		this.deviceManager = null as any;
+
 		this.tokenStore?.stop();
 		this.tokenStore?.clearState();
 		this.tokenStore?.destroy();