> ## Documentation Index
> Fetch the complete documentation index at: https://docs.rebellapp.com/llms.txt
> Use this file to discover all available pages before exploring further.

# my.onBLEConnectionStateChanged

> Listen for BLE connection state changes.

Use this API to listen for changes in a BLE device's connection state, including unexpected disconnections.

## Parameters

| Property | Type     | Required | Description                                |
| -------- | -------- | -------- | ------------------------------------------ |
| callback | Function | Yes      | Callback when the connection state changes |

## Callback Parameters

| Property  | Type    | Description                  |
| --------- | ------- | ---------------------------- |
| deviceId  | String  | The Bluetooth device ID      |
| connected | Boolean | The current connection state |

## Code Example

```javascript theme={null}
Page({
  onLoad() {
    my.onBLEConnectionStateChanged(this.handleConnectionStateChange);
  },

  handleConnectionStateChange(res) {
    if (!res.connected) {
      console.log('Device disconnected:', res.deviceId);
    }
  },

  onUnload() {
    my.offBLEConnectionStateChanged(this.handleConnectionStateChange);
  }
});
```

<Warning>
  Call `my.offBLEConnectionStateChanged` to remove any existing listener before calling `my.onBLEConnectionStateChanged`, to avoid registering duplicate listeners that each fire on the same event. IDE simulation is not supported for this API — test on a real device.
</Warning>

## Related APIs

<CardGroup cols={2}>
  <Card title="my.offBLEConnectionStateChanged" icon="xmark" href="/jsapi/device/bluetooth/my.offBLEConnectionStateChanged">
    Stop listening
  </Card>

  <Card title="my.connectBLEDevice" icon="link" href="/jsapi/device/bluetooth/my.connectBLEDevice">
    Connect to a BLE device
  </Card>
</CardGroup>