diff --git a/assets/konva/app.js b/assets/konva/app.js
index d61d948..52645a7 100644
--- a/assets/konva/app.js
+++ b/assets/konva/app.js
@@ -351,74 +351,109 @@ function _onRoomDragEnd(room, group) {
 // ---------------------------------------------------------------------------
 
 function renderSensors() {
-  sensorsLayer.destroyChildren();
+  const activeIds = new Set(
+    sensors
+      .filter(s => s.room_id != null && s.floor_x != null)
+      .map(s => `sensor-${s.id}`)
+  );
+
+  // Remove groups for sensors that are now unplaced or gone.
+  sensorsLayer.find('Group').forEach(g => {
+    if (!activeIds.has(g.id())) g.destroy();
+  });
+
   sensors.forEach(sensor => {
     if (sensor.room_id == null || sensor.floor_x == null) return;
     const room = rooms.find(r => r.id === sensor.room_id);
     if (!room) return;
 
-    const absX = (room.x + sensor.floor_x) * PPM;
-    const absY = (room.y + sensor.floor_y) * PPM;
+    const absX  = (room.x + sensor.floor_x) * PPM;
+    const absY  = (room.y + sensor.floor_y) * PPM;
     const label = sensor.name ?? sensor.sensor_id;
 
-    const group = new Konva.Group({
-      id: `sensor-${sensor.id}`,
-      x: absX, y: absY,
-      draggable: mode === 'sensorMove',
-    });
+    const existing = sensorsLayer.findOne(`#sensor-${sensor.id}`);
+    if (existing) {
+      // Update in-place — avoids the destroy-rebuild flash on drag end.
+      if (!existing.isDragging()) existing.position({ x: absX, y: absY });
+      existing.draggable(mode === 'sensorMove');
+      existing.findOne('Text')?.text(label);
+      return;
+    }
 
-    group.add(new Konva.Circle({
-      radius: 8,
-      fill: '#1565C0',
-      stroke: '#ffffff',
-      strokeWidth: 2,
-    }));
-
-    // Highlight ring — shown by highlightSensor().
-    group.add(new Konva.Circle({
-      name: 'highlight-ring',
-      radius: 14,
-      stroke: '#FDD835',
-      strokeWidth: 3,
-      visible: false,
-      listening: false,
-    }));
-
-    group.add(new Konva.Text({
-      text: label,
-      fontSize: 10,
-      fill: '#424242',
-      y: 11,
-      offsetX: 30,
-      width: 60,
-      align: 'center',
-      listening: false,
-    }));
-
-    group.on('click tap', () => {
-      if (mode === 'view') {
-        notifyFlutter({ type: 'sensorTapped', id: String(sensor.id) });
-      }
-    });
-
-    let pressTimer = null;
-    group.on('mousedown touchstart', () => {
-      if (mode === 'view') return;
-      pressTimer = setTimeout(() => {
-        notifyFlutter({ type: 'sensorTapped', id: String(sensor.id) });
-        pressTimer = null;
-      }, 500);
-    });
-    group.on('mouseup touchend touchcancel dragstart', () => {
-      clearTimeout(pressTimer);
-      pressTimer = null;
-    });
-    group.on('dragend', () => _onSensorDragEnd(sensor, group, room));
-    sensorsLayer.add(group);
+    _buildSensorGroup(sensor, absX, absY, label);
   });
   sensorsLayer.batchDraw();
 }
 
+function _buildSensorGroup(sensor, absX, absY, label) {
+  const group = new Konva.Group({
+    id: `sensor-${sensor.id}`,
+    x: absX, y: absY,
+    draggable: mode === 'sensorMove',
+  });
+
+  // Visible dot — hitFunc expands the touch target without changing appearance.
+  group.add(new Konva.Circle({
+    radius: 8,
+    fill: '#1565C0',
+    stroke: '#ffffff',
+    strokeWidth: 2,
+    hitFunc(ctx, shape) {
+      ctx.beginPath();
+      ctx.arc(0, 0, 20, 0, Math.PI * 2, true);
+      ctx.closePath();
+      ctx.fillStrokeShape(shape);
+    },
+  }));
+
+  // Highlight ring — shown by highlightSensor().
+  group.add(new Konva.Circle({
+    name: 'highlight-ring',
+    radius: 14,
+    stroke: '#FDD835',
+    strokeWidth: 3,
+    visible: false,
+    listening: false,
+  }));
+
+  group.add(new Konva.Text({
+    text: label,
+    fontSize: 10,
+    fill: '#424242',
+    y: 11,
+    offsetX: 30,
+    width: 60,
+    align: 'center',
+    listening: false,
+  }));
+
+  group.on('click tap', () => {
+    if (mode === 'view') {
+      notifyFlutter({ type: 'sensorTapped', id: String(sensor.id) });
+    }
+  });
+
+  let pressTimer = null;
+  group.on('mousedown touchstart', () => {
+    if (mode === 'view') return;
+    pressTimer = setTimeout(() => {
+      notifyFlutter({ type: 'sensorTapped', id: String(sensor.id) });
+      pressTimer = null;
+    }, 500);
+  });
+  group.on('mouseup touchend touchcancel dragstart', () => {
+    clearTimeout(pressTimer);
+    pressTimer = null;
+  });
+  // Look up the current sensor data at dragend so room_id is always fresh.
+  group.on('dragend', () => {
+    const s = sensors.find(ss => ss.id === sensor.id) ?? sensor;
+    const originalRoom = rooms.find(r => r.id === s.room_id) ?? rooms[0];
+    _onSensorDragEnd(s, group, originalRoom);
+  });
+  sensorsLayer.add(group);
+}
+
 function _onSensorDragEnd(sensor, group, originalRoom) {
   const newAbsX = group.x() / PPM;
   const newAbsY = group.y() / PPM;
@@ -427,12 +462,19 @@ function _onSensorDragEnd(sensor, group, originalRoom) {
     newAbsY >= r.y && newAbsY <= r.y + r.height,
   ) ?? originalRoom;
 
+  // Optimistically update the local sensors array so any renderSensors()
+  // call that arrives before Flutter confirms the new position via loadSensors
+  // doesn't snap the group back to the old coordinates.
+  sensor.room_id = target.id;
+  sensor.floor_x = newAbsX - target.x;
+  sensor.floor_y = newAbsY - target.y;
+
   notifyFlutter({
     type: 'sensorMoved',
     id: String(sensor.id),
     roomId: target.id,
-    x: newAbsX - target.x,
-    y: newAbsY - target.y,
+    x: sensor.floor_x,
+    y: sensor.floor_y,
   });
 }