diff --git a/visionA-frontend/src/stores/device-store.test.ts b/visionA-frontend/src/stores/device-store.test.ts
index b996fda..b9a316d 100644
--- a/visionA-frontend/src/stores/device-store.test.ts
+++ b/visionA-frontend/src/stores/device-store.test.ts
@@ -175,7 +175,7 @@ describe("useDeviceStore", () => {
     });
   });
 
-  it("serial_number 正規化：snake_case / camelCase 都吃、缺欄位與空字串 → null（WP-C）", async () => {
+  it("serial_number 正規化：snake_case / camelCase 都吃、缺欄位與空字串／純空白 → null（WP-C）", async () => {
     vi.spyOn(globalThis, "fetch").mockResolvedValueOnce(
       jsonResponse({
         success: true,
@@ -188,6 +188,8 @@ describe("useDeviceStore", () => {
           { id: "dev-3", name: "C", type: "kl520", status: "connected" },
           // 空字串（防禦性；無法路由）→ null
           { id: "dev-4", name: "D", type: "kl520", status: "connected", serial_number: "" },
+          // 純空白（防禦性；trim 後為空、無法路由）→ null
+          { id: "dev-5", name: "E", type: "kl520", status: "connected", serial_number: "   " },
         ],
       }),
     );
@@ -198,6 +200,7 @@ describe("useDeviceStore", () => {
     expect(devices[1]?.serialNumber).toBe("KN99887766");
     expect(devices[2]?.serialNumber).toBeNull();
     expect(devices[3]?.serialNumber).toBeNull();
+    expect(devices[4]?.serialNumber).toBeNull();
   });
 
   it("fetchDevices 遇到 501 NOT_IMPLEMENTED 時視為空 list，不記錯誤", async () => {
diff --git a/visionA-frontend/src/stores/device-store.ts b/visionA-frontend/src/stores/device-store.ts
index ed03cf1..8114168 100644
--- a/visionA-frontend/src/stores/device-store.ts
+++ b/visionA-frontend/src/stores/device-store.ts
@@ -112,14 +112,16 @@ function normalizeDevice(raw: unknown): Device {
   const rawRemoteStatus = pick<string>("remote_status", "remoteStatus") as
     | RemoteStatus
     | undefined;
-  // serial_number 為 omitempty：缺欄位 → null；防禦性把空字串也視為 null
-  // （空字串無法路由，語意上等同「未回報序號」）。
+  // serial_number 為 omitempty：缺欄位 → null；防禦性把空字串／純空白也視為 null
+  // （空字串與空白皆無法路由，語意上等同「未回報序號」）。先 trim 再判定，
+  // 避免純空白（" "）誤判為 truthy 而以空白 serial 組出必失敗的請求路由。
   const rawSerial = pick<string>("serial_number", "serialNumber");
+  const serial = rawSerial != null ? String(rawSerial).trim() : "";
   return {
     id: String(pick<string>("id") ?? ""),
     name: String(pick<string>("name") ?? pick<string>("device_name") ?? ""),
     alias: pick<string>("alias") ?? undefined,
-    serialNumber: rawSerial ? String(rawSerial) : null,
+    serialNumber: serial !== "" ? serial : null,
     type: String(pick<string>("type", "device_type") ?? ""),
     status: (pick<string>("status") as DeviceHardwareStatus) ?? "disconnected",
     remoteStatus: