diff --git a/jsonrpc.go b/jsonrpc.go
index 5a662530d..049a67601 100644
--- a/jsonrpc.go
+++ b/jsonrpc.go
@@ -880,12 +880,16 @@ func rpcSetATXPowerAction(action string) error {
 type ATXState struct {
 	Power bool `json:"power"`
 	HDD   bool `json:"hdd"`
+	// Responsive reports whether the ATX extension board has sent a status
+	// line recently, so the UI can flag an unpowered or disconnected board.
+	Responsive bool `json:"responsive"`
 }
 
 func rpcGetATXState() (ATXState, error) {
 	state := ATXState{
-		Power: ledPWRState.Load(),
-		HDD:   ledHDDState.Load(),
+		Power:      ledPWRState.Load(),
+		HDD:        ledHDDState.Load(),
+		Responsive: atxBoardResponsive(),
 	}
 	return state, nil
 }
diff --git a/mqtt.go b/mqtt.go
index 9c9e2f199..019b19d6a 100644
--- a/mqtt.go
+++ b/mqtt.go
@@ -204,8 +204,9 @@ func (m *MQTTManager) onConnect(client mqtt.Client) {
 	// the current state of all switches and sensors right away.
 	if config.ActiveExtension == "atx-power" {
 		m.publishATXState(ATXState{
-			Power: ledPWRState.Load(),
-			HDD:   ledHDDState.Load(),
+			Power:      ledPWRState.Load(),
+			HDD:        ledHDDState.Load(),
+			Responsive: atxBoardResponsive(),
 		})
 	}
 	if config.ActiveExtension == "dc-power" {
diff --git a/mqtt_publish.go b/mqtt_publish.go
index fc2818c40..c9f6e5185 100644
--- a/mqtt_publish.go
+++ b/mqtt_publish.go
@@ -563,8 +563,9 @@ func (m *MQTTManager) startPeriodicStatusUpdates(interval time.Duration) {
 				// Publish current ATX state only if ATX extension is active
 				if config.ActiveExtension == "atx-power" {
 					m.publishATXState(ATXState{
-						Power: ledPWRState.Load(),
-						HDD:   ledHDDState.Load(),
+						Power:      ledPWRState.Load(),
+						HDD:        ledHDDState.Load(),
+						Responsive: atxBoardResponsive(),
 					})
 				}
 
diff --git a/serial.go b/serial.go
index 6189c1e03..8214e4cfc 100644
--- a/serial.go
+++ b/serial.go
@@ -23,6 +23,7 @@ var consoleBroker *ConsoleBroker
 
 func mountATXControl() error {
 	_ = port.SetMode(defaultMode)
+	atxLastLineTime.Store(0)
 	go runATXControl()
 
 	return nil
@@ -38,8 +39,24 @@ var (
 	ledPWRState atomic.Bool
 	btnRSTState bool
 	btnPWRState bool
+
+	// atxLastLineTime holds the unix time (in seconds) of the last status
+	// line received from the ATX extension board. Zero means no line has
+	// been received since the extension was mounted.
+	atxLastLineTime atomic.Int64
 )
 
+// atxResponsiveTimeout is how long after the last received status line the
+// ATX extension board is still considered responsive.
+const atxResponsiveTimeout = 10 * time.Second
+
+// atxBoardResponsive reports whether the ATX extension board has sent a
+// status line within atxResponsiveTimeout.
+func atxBoardResponsive() bool {
+	lastLine := atxLastLineTime.Load()
+	return lastLine != 0 && time.Since(time.Unix(lastLine, 0)) < atxResponsiveTimeout
+}
+
 func runATXControl() {
 	scopedLogger := serialLogger.With().Str("service", "atx_control").Logger()
 
@@ -51,6 +68,9 @@ func runATXControl() {
 			return
 		}
 
+		// The board is talking to us, even if the line turns out invalid.
+		atxLastLineTime.Store(time.Now().Unix())
+
 		// Each line should be 4 binary digits + newline
 		if len(line) != 5 {
 			scopedLogger.Warn().Int("length", len(line)).Msg("Invalid line length")
@@ -64,8 +84,9 @@ func runATXControl() {
 		newBtnPWRState := line[3] == '1'
 
 		atxState := ATXState{
-			Power: newLedPWRState,
-			HDD:   newLedHDDState,
+			Power:      newLedPWRState,
+			HDD:        newLedHDDState,
+			Responsive: true, // a status line was just received
 		}
 
 		if currentSession != nil {
diff --git a/ui/localization/messages/cy.json b/ui/localization/messages/cy.json
index cb22b38b1..d9fc10032 100644
--- a/ui/localization/messages/cy.json
+++ b/ui/localization/messages/cy.json
@@ -150,6 +150,7 @@
     "appearance_theme_system": "System",
     "appearance_title": "Ymddangosiad",
     "attach": "Atodi",
+    "atx_power_control_board_not_responding": "Dim ymateb gan y bwrdd estyniad ATX. Gwiriwch y cebl RJ-12 a phŵer y bwrdd.",
     "atx_power_control_get_state_error": "Methwyd cael cyflwr pŵer ATX: {error}",
     "atx_power_control_hdd_led": "LED HDD",
     "atx_power_control_hold_hint": "Dal am 3 eiliad i orfodi diffodd",
diff --git a/ui/localization/messages/da.json b/ui/localization/messages/da.json
index 075a91f5e..4bbe07588 100644
--- a/ui/localization/messages/da.json
+++ b/ui/localization/messages/da.json
@@ -155,6 +155,7 @@
     "appearance_theme_system": "System",
     "appearance_title": "Udseende",
     "attach": "Vedhæft",
+    "atx_power_control_board_not_responding": "Intet svar fra ATX-udvidelseskortet. Kontrollér RJ-12-kablet og kortets strømforsyning.",
     "atx_power_control_get_state_error": "Kunne ikke hente ATX-strømtilstand: {error}",
     "atx_power_control_hdd_led": "HDD-LED",
     "atx_power_control_hold_hint": "Hold nede i 3 sek. for at tvinge slukning",
diff --git a/ui/localization/messages/de.json b/ui/localization/messages/de.json
index 0b89ef173..c4bcefc16 100644
--- a/ui/localization/messages/de.json
+++ b/ui/localization/messages/de.json
@@ -155,6 +155,7 @@
     "appearance_theme_system": "System",
     "appearance_title": "Darstellung",
     "attach": "Anhängen",
+    "atx_power_control_board_not_responding": "Keine Antwort von der ATX-Erweiterungsplatine. Prüfen Sie das RJ-12-Kabel und die Stromversorgung der Platine.",
     "atx_power_control_get_state_error": "ATX-Stromversorgungsstatus konnte nicht abgerufen werden: {error}",
     "atx_power_control_hdd_led": "Festplatten-LED",
     "atx_power_control_hold_hint": "3 Sekunden halten zum Ausschalten erzwingen",
diff --git a/ui/localization/messages/en.json b/ui/localization/messages/en.json
index 63be6e8d9..be749dc2c 100644
--- a/ui/localization/messages/en.json
+++ b/ui/localization/messages/en.json
@@ -155,6 +155,7 @@
     "appearance_theme_system": "System",
     "appearance_title": "Appearance",
     "attach": "Attach",
+    "atx_power_control_board_not_responding": "No response from the ATX extension board. Check the RJ-12 cable and board power.",
     "atx_power_control_get_state_error": "Failed to get ATX power state: {error}",
     "atx_power_control_hdd_led": "HDD LED",
     "atx_power_control_hold_hint": "Hold for 3s to force off",
diff --git a/ui/localization/messages/es.json b/ui/localization/messages/es.json
index fa9aa1b69..5d098289f 100644
--- a/ui/localization/messages/es.json
+++ b/ui/localization/messages/es.json
@@ -155,6 +155,7 @@
     "appearance_theme_system": "Sistema",
     "appearance_title": "Apariencia",
     "attach": "Adjuntar",
+    "atx_power_control_board_not_responding": "No hay respuesta de la placa de extensión ATX. Compruebe el cable RJ-12 y la alimentación de la placa.",
     "atx_power_control_get_state_error": "No se pudo obtener el estado de energía ATX: {error}",
     "atx_power_control_hdd_led": "LED del disco duro",
     "atx_power_control_hold_hint": "Mantenga presionado 3 s para forzar el apagado",
diff --git a/ui/localization/messages/fr.json b/ui/localization/messages/fr.json
index 226a66f28..6b513d339 100644
--- a/ui/localization/messages/fr.json
+++ b/ui/localization/messages/fr.json
@@ -155,6 +155,7 @@
     "appearance_theme_system": "Système",
     "appearance_title": "Apparence",
     "attach": "Attacher",
+    "atx_power_control_board_not_responding": "Aucune réponse de la carte d'extension ATX. Vérifiez le câble RJ-12 et l'alimentation de la carte.",
     "atx_power_control_get_state_error": "Échec de l'obtention de l'état d'alimentation ATX : {error}",
     "atx_power_control_hdd_led": "Voyant du disque dur",
     "atx_power_control_hold_hint": "Maintenir 3 s pour forcer l'arrêt",
diff --git a/ui/localization/messages/it.json b/ui/localization/messages/it.json
index 2c52f2d57..b324e4daa 100644
--- a/ui/localization/messages/it.json
+++ b/ui/localization/messages/it.json
@@ -155,6 +155,7 @@
     "appearance_theme_system": "Sistema",
     "appearance_title": "Aspetto",
     "attach": "Allega",
+    "atx_power_control_board_not_responding": "Nessuna risposta dalla scheda di estensione ATX. Controlla il cavo RJ-12 e l'alimentazione della scheda.",
     "atx_power_control_get_state_error": "Impossibile ottenere lo stato di alimentazione ATX: {error}",
     "atx_power_control_hdd_led": "LED dell'HDD",
     "atx_power_control_hold_hint": "Tenere premuto 3 s per lo spegnimento forzato",
diff --git a/ui/localization/messages/ja.json b/ui/localization/messages/ja.json
index 629d14133..dceed065d 100644
--- a/ui/localization/messages/ja.json
+++ b/ui/localization/messages/ja.json
@@ -155,6 +155,7 @@
     "appearance_theme_system": "システム",
     "appearance_title": "外観",
     "attach": "接続",
+    "atx_power_control_board_not_responding": "ATX拡張ボードから応答がありません。RJ-12ケーブルとボードの電源を確認してください。",
     "atx_power_control_get_state_error": "ATX電源状態の取得に失敗しました: {error}",
     "atx_power_control_hdd_led": "HDD LED",
     "atx_power_control_hold_hint": "3秒長押しで強制オフ",
diff --git a/ui/localization/messages/nb.json b/ui/localization/messages/nb.json
index c7791e12c..6f2faceff 100644
--- a/ui/localization/messages/nb.json
+++ b/ui/localization/messages/nb.json
@@ -155,6 +155,7 @@
     "appearance_theme_system": "System",
     "appearance_title": "Utseende",
     "attach": "Legg ved",
+    "atx_power_control_board_not_responding": "Ingen respons fra ATX-utvidelseskortet. Kontroller RJ-12-kabelen og strømforsyningen til kortet.",
     "atx_power_control_get_state_error": "Klarte ikke å hente ATX-strømstatus: {error}",
     "atx_power_control_hdd_led": "HDD-LED",
     "atx_power_control_hold_hint": "Hold inne 3 s for å tvinge avslåing",
diff --git a/ui/localization/messages/pt.json b/ui/localization/messages/pt.json
index 16157e922..71741db86 100644
--- a/ui/localization/messages/pt.json
+++ b/ui/localization/messages/pt.json
@@ -155,6 +155,7 @@
     "appearance_theme_system": "Sistema",
     "appearance_title": "Aparência",
     "attach": "Anexar",
+    "atx_power_control_board_not_responding": "Sem resposta da placa de extensão ATX. Verifique o cabo RJ-12 e a alimentação da placa.",
     "atx_power_control_get_state_error": "Falha ao obter estado de energia ATX: {error}",
     "atx_power_control_hdd_led": "LED do HDD",
     "atx_power_control_hold_hint": "Manter premido 3 s para forçar o desligamento",
diff --git a/ui/localization/messages/ru.json b/ui/localization/messages/ru.json
index a14b709cd..c83852c84 100644
--- a/ui/localization/messages/ru.json
+++ b/ui/localization/messages/ru.json
@@ -155,6 +155,7 @@
     "appearance_theme_system": "Системная",
     "appearance_title": "Внешний вид",
     "attach": "Подключить",
+    "atx_power_control_board_not_responding": "Нет ответа от платы расширения ATX. Проверьте кабель RJ-12 и питание платы.",
     "atx_power_control_get_state_error": "Не удалось получить состояние ATX-питания: {error}",
     "atx_power_control_hdd_led": "Индикатор HDD",
     "atx_power_control_hold_hint": "Удерживайте 3 с для принудительного выключения",
diff --git a/ui/localization/messages/sv.json b/ui/localization/messages/sv.json
index 2560ca511..2fe4a6326 100644
--- a/ui/localization/messages/sv.json
+++ b/ui/localization/messages/sv.json
@@ -155,6 +155,7 @@
     "appearance_theme_system": "System",
     "appearance_title": "Utseende",
     "attach": "Bifoga",
+    "atx_power_control_board_not_responding": "Inget svar från ATX-expansionskortet. Kontrollera RJ-12-kabeln och kortets strömförsörjning.",
     "atx_power_control_get_state_error": "Misslyckades med att hämta ATX-strömstatus: {error}",
     "atx_power_control_hdd_led": "Hårddisk-LED",
     "atx_power_control_hold_hint": "Håll in 3 s för att tvinga avstängning",
diff --git a/ui/localization/messages/zh-tw.json b/ui/localization/messages/zh-tw.json
index cdc15781f..6fe875d85 100644
--- a/ui/localization/messages/zh-tw.json
+++ b/ui/localization/messages/zh-tw.json
@@ -155,6 +155,7 @@
     "appearance_theme_system": "系統",
     "appearance_title": "外觀",
     "attach": "放至下方",
+    "atx_power_control_board_not_responding": "ATX 擴充板沒有回應。請檢查 RJ-12 線材與擴充板的電源。",
     "atx_power_control_get_state_error": "取得 ATX 電源狀態失敗：{error}",
     "atx_power_control_hdd_led": "HDD 指示燈",
     "atx_power_control_hold_hint": "按住 3 秒強制關機",
diff --git a/ui/localization/messages/zh.json b/ui/localization/messages/zh.json
index ce4604bd7..c25021c89 100644
--- a/ui/localization/messages/zh.json
+++ b/ui/localization/messages/zh.json
@@ -155,6 +155,7 @@
     "appearance_theme_system": "跟随系统",
     "appearance_title": "外观",
     "attach": "挂载",
+    "atx_power_control_board_not_responding": "ATX 扩展板无响应。请检查 RJ-12 线缆和扩展板的电源。",
     "atx_power_control_get_state_error": "获取 ATX 电源状态失败：{error}",
     "atx_power_control_hdd_led": "硬盘指示灯",
     "atx_power_control_hold_hint": "按住 3 秒强制关机",
diff --git a/ui/src/components/extensions/ATXPowerControl.tsx b/ui/src/components/extensions/ATXPowerControl.tsx
index 2b644935a..4cc397b7b 100644
--- a/ui/src/components/extensions/ATXPowerControl.tsx
+++ b/ui/src/components/extensions/ATXPowerControl.tsx
@@ -1,5 +1,5 @@
 import { useEffect, useState } from "react";
-import { LuHardDrive, LuPower, LuRotateCcw } from "react-icons/lu";
+import { LuHardDrive, LuPower, LuRotateCcw, LuTriangleAlert } from "react-icons/lu";
 
 import { m } from "@localizations/messages.js";
 import { JsonRpcResponse, useJsonRpc } from "@hooks/useJsonRpc";
@@ -10,10 +10,12 @@ import { SettingsPageHeader } from "@components/SettingsPageheader";
 import notifications from "@/notifications";
 
 const LONG_PRESS_DURATION = 3000; // 3 seconds for long press
+const STATE_POLL_INTERVAL = 5000; // Poll board responsiveness every 5 seconds
 
 interface ATXState {
   power: boolean;
   hdd: boolean;
+  responsive?: boolean;
 }
 
 export function ATXPowerControl() {
@@ -29,17 +31,26 @@ export function ATXPowerControl() {
     }
   });
 
-  // Request initial state
+  // Request initial state and keep polling while the control is open,
+  // so an unresponsive extension board is detected and surfaced.
   useEffect(() => {
-    send("getATXState", {}, (resp: JsonRpcResponse) => {
-      if ("error" in resp) {
-        notifications.error(
-          m.atx_power_control_get_state_error({ error: resp.error.data || m.unknown_error() }),
-        );
-        return;
-      }
-      setAtxState(resp.result as ATXState);
-    });
+    const requestState = (notifyOnError: boolean) => {
+      send("getATXState", {}, (resp: JsonRpcResponse) => {
+        if ("error" in resp) {
+          if (notifyOnError) {
+            notifications.error(
+              m.atx_power_control_get_state_error({ error: resp.error.data || m.unknown_error() }),
+            );
+          }
+          return;
+        }
+        setAtxState(resp.result as ATXState);
+      });
+    };
+
+    requestState(true);
+    const pollTimer = setInterval(() => requestState(false), STATE_POLL_INTERVAL);
+    return () => clearInterval(pollTimer);
   }, [send]);
 
   const handlePowerPress = (pressed: boolean) => {
@@ -115,6 +126,13 @@ export function ATXPowerControl() {
       ) : (
         <Card className="min-h-[120px] animate-fadeIn opacity-0">
           <div className="space-y-4 p-3">
+            {/* Board responsiveness warning */}
+            {atxState.responsive === false && (
+              <div className="flex items-start gap-x-2 text-xs text-amber-600 dark:text-amber-500">
+                <LuTriangleAlert className="mt-0.5 h-4 w-4 shrink-0" />
+                <span>{m.atx_power_control_board_not_responding()}</span>
+              </div>
+            )}
             {/* Control Buttons */}
             <div className="flex items-center space-x-2">
               <Button
@@ -147,7 +165,9 @@ export function ATXPowerControl() {
                 }}
               />
             </div>
-            <p className="text-xs text-slate-500 dark:text-slate-400">{m.atx_power_control_hold_hint()}</p>
+            <p className="text-xs text-slate-500 dark:text-slate-400">
+              {m.atx_power_control_hold_hint()}
+            </p>
 
             <hr className="border-slate-700/30 dark:border-slate-600/30" />
             {/* Status Indicators */}