diff --git a/frontend/src/__tests__/issue-270-firmware-wifi-note.test.ts b/frontend/src/__tests__/issue-270-firmware-wifi-note.test.ts
index 49cd711f..4ba1b8c0 100644
--- a/frontend/src/__tests__/issue-270-firmware-wifi-note.test.ts
+++ b/frontend/src/__tests__/issue-270-firmware-wifi-note.test.ts
@@ -29,14 +29,14 @@ function image(strings: string[]): File {
 
 describe('issue #270 — uploaded firmware that cannot reach any network', () => {
   it('warns when the image uses WiFi and names no reachable network', async () => {
-    const note = await wifiSsidNoteFor(image(['WiFiGeneric', 'MyHomeNet']));
+    const note = await wifiSsidNoteFor(image(['net80211', 'esp_wifi', 'MyHomeNet']));
     expect(note).toBeTruthy();
     for (const ssid of EMULATED_WIFI_SSIDS) expect(note).toContain(ssid);
   });
 
   it('stays quiet when the image already names one', async () => {
     for (const ssid of EMULATED_WIFI_SSIDS) {
-      expect(await wifiSsidNoteFor(image(['WiFiGeneric', ssid]))).toBeNull();
+      expect(await wifiSsidNoteFor(image(['net80211', 'esp_wifi', ssid]))).toBeNull();
     }
   });
 
@@ -46,17 +46,74 @@ describe('issue #270 — uploaded firmware that cannot reach any network', () =>
     expect(await wifiSsidNoteFor(image(['blink', 'digitalWrite']))).toBeNull();
   });
 
+  it('stays quiet for the reporter\'s own binary, which names the right network', async () => {
+    // His SSID was correct all along — the note must not accuse him of a
+    // problem he does not have.
+    expect(await wifiSsidNoteFor(image(['net80211', 'esp_wifi', 'Velxio-GUEST']))).toBeNull();
+  });
+
   it('recognises the WiFi stack by more than one marker', async () => {
-    for (const marker of ['WiFiGeneric', 'STA.cpp', 'esp_wifi_connect', 'wifi_station']) {
+    for (const marker of ['net80211', 'phy_init', 'esp_wifi', 'wifi_init']) {
       expect(await wifiSsidNoteFor(image([marker, 'SomeHomeNet']))).toBeTruthy();
     }
   });
 
+  it('still recognises it when the build stripped its log strings', async () => {
+    // The reporter's second binary has no 'STA.cpp' and no 'WiFiGeneric' at
+    // all — a lower debug level drops them — while the driver names remain.
+    // Keying on the log strings meant the note stayed silent on exactly the
+    // firmware it exists for.
+    const stripped = image(['net80211', 'phy_init', 'esp_wifi', 'MyHomeNet']);
+    expect(await wifiSsidNoteFor(stripped)).toBeTruthy();
+  });
+
+  it('does not fire on a name that a blink image also carries', async () => {
+    // WIFI_INIT is in both a blink build and a WiFi build, measured.
+    expect(await wifiSsidNoteFor(image(['WIFI_INIT_CONFIG_DEFAULT', 'blink']))).toBeNull();
+  });
+
   it('finds a marker that straddles the very end of the image', async () => {
     const bytes: number[] = [];
     for (let i = 0; i < 100; i++) bytes.push(0xff);
-    for (const ch of 'WiFiGeneric') bytes.push(ch.charCodeAt(0));
+    for (const ch of 'net80211') bytes.push(ch.charCodeAt(0));
     const note = await wifiSsidNoteFor(new File([new Uint8Array(bytes)], 'fw.bin'));
     expect(note).toBeTruthy();
   });
 });
+
+describe('issue #270 — the serial note for a blank-NVS connect', () => {
+  // Verified against the emulator: WiFi.begin() with no arguments on the
+  // simulator's blank flash produces exactly `STA.cpp:357 ... 0x300a:
+  // ESP_ERR_WIFI_SSID` — the reporter's error, timestamps and all. On his
+  // real DevKit the same binary worked because NVS still held credentials
+  // some earlier firmware had saved.
+  const MARKER = '0x300a: ESP_ERR_WIFI_SSID';
+
+  it('explains the error once', async () => {
+    const { annotateSerialChunk } = await import('../utils/serialDiagnostics');
+    const chunk = `[  40][E][STA.cpp:357] connect(): STA connect failed! ${MARKER}\r\n`;
+    const out = annotateSerialChunk('', chunk);
+    expect(out).toContain('NVS');
+    expect(out).toContain('Velxio-GUEST');
+  });
+
+  it('does not repeat itself while the same run keeps failing', async () => {
+    const { annotateSerialChunk } = await import('../utils/serialDiagnostics');
+    const chunk = `STA connect failed! ${MARKER}\r\n`;
+    const first = annotateSerialChunk('', chunk);
+    const second = annotateSerialChunk(first, chunk);
+    expect(second).not.toContain('NVS');
+  });
+
+  it('re-arms on a fresh run, whose log starts empty', async () => {
+    const { annotateSerialChunk } = await import('../utils/serialDiagnostics');
+    const chunk = `STA connect failed! ${MARKER}\r\n`;
+    annotateSerialChunk('', chunk);
+    expect(annotateSerialChunk('', chunk)).toContain('NVS');
+  });
+
+  it('leaves ordinary output alone', async () => {
+    const { annotateSerialChunk } = await import('../utils/serialDiagnostics');
+    expect(annotateSerialChunk('', 'TICK 1\r\n')).toBe('TICK 1\r\n');
+  });
+});
diff --git a/frontend/src/store/useSimulatorStore.ts b/frontend/src/store/useSimulatorStore.ts
index 030f9657..6244a5a5 100644
--- a/frontend/src/store/useSimulatorStore.ts
+++ b/frontend/src/store/useSimulatorStore.ts
@@ -28,6 +28,7 @@ import type { RP2040I2CDevice } from '../simulation/RP2040Simulator';
 import type { Wire, WireInProgress, WireEndpoint } from '../types/wire';
 import type { BoardKind, BoardInstance, LanguageMode, WifiStatus } from '../types/board';
 import { BOARD_KIND_FQBN, BOARD_SUPPORTS_ESPIDF, BOARD_SUPPORTS_MICROPYTHON, EMULATED_WIFI_SSIDS, isPiBoardKind, isStm32BoardKind } from '../types/board';
+import { annotateSerialChunk } from '../utils/serialDiagnostics';
 import { boardGateDecision, proBoardFeatureName, triggerProUpgradePrompt } from '../lib/proBoardGate';
 import { getSerialTxInterceptor } from '../lib/proHardwareSerial';
 import { calculatePinPosition } from '../utils/pinPositionCalculator';
@@ -1312,8 +1313,11 @@ const { append: appendSerial } = createSerialBatcher((perBoard) => {
   useSimulatorStore.setState((s) => {
     let globalOut = s.serialOutput;
     const boards = s.boards.map((b) => {
-      const chunk = perBoard.get(b.id);
-      if (!chunk) return b;
+      const raw = perBoard.get(b.id);
+      if (!raw) return b;
+      // Attach the one-line explanation when a known cryptic firmware error
+      // scrolls past (issue #270); a no-op for ordinary output.
+      const chunk = annotateSerialChunk(b.serialOutput, raw);
       if (s.activeBoardId === b.id) globalOut += chunk;
       return { ...b, serialOutput: b.serialOutput + chunk };
     });
diff --git a/frontend/src/utils/firmwareWifiNote.ts b/frontend/src/utils/firmwareWifiNote.ts
index 02c57536..f7852895 100644
--- a/frontend/src/utils/firmwareWifiNote.ts
+++ b/frontend/src/utils/firmwareWifiNote.ts
@@ -13,12 +13,20 @@
 import { EMULATED_WIFI_SSIDS } from '../types/board';
 
 /**
- * Markers that the image contains the Arduino WiFi stack. Kept narrow on
- * purpose: `esp_wifi` alone appears in images that never touch the radio, and
- * a note shown to someone who does not need it is noise that teaches people to
- * ignore the console.
+ * Markers that the image links the WiFi stack.
+ *
+ * Chosen by measurement, against two real builds of the same board: a blink
+ * sketch and a WiFi one. Every name here is absent from the blink image and
+ * present in the WiFi one. `WIFI_INIT` looked obvious and is in BOTH, so it is
+ * not here.
+ *
+ * They are IDF-level names on purpose. The first version of this list used the
+ * Arduino log strings ('WiFiGeneric', 'STA.cpp'), which vanish when the build
+ * lowers its debug level — the reporter's own second binary has neither, and
+ * the note would have stayed silent on the exact firmware it was written for.
+ * These survive, because they are the driver, not a message about it.
  */
-const WIFI_MARKERS = ['WiFiGeneric', 'STA.cpp', 'esp_wifi_connect', 'wifi_station'];
+const WIFI_MARKERS = ['net80211', 'phy_init', 'esp_wifi', 'wifi_init'];
 
 /** Search a binary for an ASCII string, without decoding the whole image. */
 function containsAscii(bytes: Uint8Array, needle: string): boolean {
diff --git a/frontend/src/utils/serialDiagnostics.ts b/frontend/src/utils/serialDiagnostics.ts
new file mode 100644
index 00000000..1f430ae1
--- /dev/null
+++ b/frontend/src/utils/serialDiagnostics.ts
@@ -0,0 +1,39 @@
+/**
+ * One-line explanations for serial errors that read as emulator bugs.
+ *
+ * The firmware's own message is written for someone holding real hardware.
+ * `ESP_ERR_WIFI_SSID` cost the reporter of issue #270 days: his Visuino build
+ * called WiFi.begin() with no credentials, which on a real DevKit quietly
+ * reuses the network saved in the chip's flash (NVS) by some earlier firmware
+ * — and the simulator's flash starts blank, so the same binary fails at boot
+ * with a hex code. Nothing was wrong with the emulation; nothing in the output
+ * said so.
+ *
+ * Each entry appends its note once per run: the note re-arms when the serial
+ * log is cleared (every Run starts a fresh log), because the presence of the
+ * note in the existing output is itself the marker.
+ */
+const NOTES: ReadonlyArray<{ marker: string; note: string }> = [
+  {
+    marker: '0x300a: ESP_ERR_WIFI_SSID',
+    note:
+      '[velxio] This firmware asked to connect with no SSID (or an invalid one). ' +
+      'WiFi.begin() without arguments reuses credentials saved in the chip’s flash (NVS) ' +
+      'by a previous firmware — the simulator’s flash starts blank, so there is nothing ' +
+      'to reuse. Pass them explicitly: WiFi.begin("Velxio-GUEST", "").',
+  },
+];
+
+/**
+ * The chunk to actually append, with any due explanation attached. Pure so it
+ * can be tested without the frame batcher around it.
+ */
+export function annotateSerialChunk(existingOutput: string, chunk: string): string {
+  let out = chunk;
+  for (const { marker, note } of NOTES) {
+    if (out.includes(marker) && !existingOutput.includes(note) && !out.includes(note)) {
+      out += `\r\n${note}\r\n`;
+    }
+  }
+  return out;
+}