diff --git a/frontend/src/components/simulator/SensorControlPanel.tsx b/frontend/src/components/simulator/SensorControlPanel.tsx
index f7e97e6f..7824545d 100644
--- a/frontend/src/components/simulator/SensorControlPanel.tsx
+++ b/frontend/src/components/simulator/SensorControlPanel.tsx
@@ -13,7 +13,7 @@ import {
   type SensorControl,
   type SliderControl,
 } from '../../simulation/sensorControlConfig';
-import { dispatchSensorUpdate } from '../../simulation/SensorUpdateRegistry';
+import { dispatchSensorUpdate, getLastSensorValues } from '../../simulation/SensorUpdateRegistry';
 import './SensorControlPanel.css';
 
 interface SensorControlPanelProps {
@@ -51,14 +51,22 @@ export const SensorControlPanel: React.FC<SensorControlPanelProps> = ({
   const { t } = useTranslation();
   const def = SENSOR_CONTROLS[metadataId];
 
-  // Local slider/button state — initialised from config defaults
-  const [values, setValues] = useState<Record<string, number | boolean>>(
-    def ? { ...def.defaultValues } : {},
-  );
+  // Local slider/button state — hydrated from the registry's last-known
+  // values for this componentId (so reopening a sensor or switching between
+  // two sensors of the same type shows each one's current state, not the
+  // previous panel's). Falls back to config defaults the first time a
+  // sensor is opened.
+  const [values, setValues] = useState<Record<string, number | boolean>>(() => {
+    const cached = getLastSensorValues(componentId);
+    if (cached) return { ...(def?.defaultValues ?? {}), ...cached };
+    return def ? { ...def.defaultValues } : {};
+  });
 
-  // Push initial defaults into simulation on mount
+  // Push defaults into simulation on first open for this sensor. Skipped
+  // when the sensor already has cached values — the simulation still holds
+  // them, no need to clobber.
   useEffect(() => {
-    if (def && Object.keys(def.defaultValues).length > 0) {
+    if (def && Object.keys(def.defaultValues).length > 0 && !getLastSensorValues(componentId)) {
       dispatchSensorUpdate(componentId, def.defaultValues);
     }
     // eslint-disable-next-line react-hooks/exhaustive-deps
diff --git a/frontend/src/components/simulator/SimulatorCanvas.tsx b/frontend/src/components/simulator/SimulatorCanvas.tsx
index 462b9524..16551091 100644
--- a/frontend/src/components/simulator/SimulatorCanvas.tsx
+++ b/frontend/src/components/simulator/SimulatorCanvas.tsx
@@ -2382,13 +2382,18 @@ export const SimulatorCanvas = ({ headerSlot }: SimulatorCanvasProps = {}) => {
                   : 'default',
           }}
         >
-          {/* Sensor Control Panel — shown when a sensor component is clicked during simulation */}
+          {/* Sensor Control Panel — shown when a sensor component is clicked during simulation.
+              key={sensorControlComponentId} forces a fresh mount when the user clicks a
+              different instance of the same sensor type (e.g. a second photoresistor); the
+              slider state is local and would otherwise show the previously-clicked sensor's
+              value until the user manually moved it. */}
           {sensorControlComponentId &&
             sensorControlMetadataId &&
             (() => {
               const meta = registry.getById(sensorControlMetadataId);
               return (
                 <SensorControlPanel
+                  key={sensorControlComponentId}
                   componentId={sensorControlComponentId}
                   metadataId={sensorControlMetadataId}
                   sensorName={meta?.name ?? sensorControlMetadataId}
diff --git a/frontend/src/simulation/SensorUpdateRegistry.ts b/frontend/src/simulation/SensorUpdateRegistry.ts
index 88119898..626a0e2e 100644
--- a/frontend/src/simulation/SensorUpdateRegistry.ts
+++ b/frontend/src/simulation/SensorUpdateRegistry.ts
@@ -6,9 +6,11 @@
  * running simulation without any React/Zustand dependency in the simulation layer.
  */
 
-type SensorUpdateCallback = (values: Record<string, number | boolean>) => void;
+type SensorValues = Record<string, number | boolean>;
+type SensorUpdateCallback = (values: SensorValues) => void;
 
 const registry = new Map<string, SensorUpdateCallback>();
+const lastValues = new Map<string, SensorValues>();
 
 /**
  * Register a callback for a component. Called from inside attachEvents().
@@ -20,19 +22,31 @@ export function registerSensorUpdate(componentId: string, cb: SensorUpdateCallba
 
 /**
  * Dispatch new sensor values for a component. Called from SensorControlPanel.
- * No-ops silently if the component has no registered callback.
+ * No-ops silently if the component has no registered callback. Values are
+ * also cached so the panel can rehydrate the slider when reopened on the
+ * same sensor (or when switching between sensors of the same type).
  */
-export function dispatchSensorUpdate(
-  componentId: string,
-  values: Record<string, number | boolean>,
-): void {
+export function dispatchSensorUpdate(componentId: string, values: SensorValues): void {
   registry.get(componentId)?.(values);
+  const prev = lastValues.get(componentId);
+  lastValues.set(componentId, prev ? { ...prev, ...values } : { ...values });
+}
+
+/**
+ * Read the last values dispatched for a component. Returns undefined if the
+ * component has never received a dispatch. Used by SensorControlPanel to
+ * restore slider state when reopened.
+ */
+export function getLastSensorValues(componentId: string): SensorValues | undefined {
+  return lastValues.get(componentId);
 }
 
 /**
  * Unregister a component's callback. Called in the cleanup function returned
  * by attachEvents() so stale callbacks don't persist after simulation stops.
+ * Values are also cleared so a deleted/recreated component starts fresh.
  */
 export function unregisterSensorUpdate(componentId: string): void {
   registry.delete(componentId);
+  lastValues.delete(componentId);
 }