> ## 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.onBLECharacteristicValueChange
> Listen for BLE characteristic value changes.
Use this API to listen for changes in the value of a BLE device characteristic. It is triggered when you call `my.readBLECharacteristicValue` or when a characteristic with `notify` or `indicate` enabled pushes a new value.
## Parameters
| Property | Type | Required | Description |
| -------- | -------- | -------- | -------------------------------------------- |
| success | Function | No | Callback when a characteristic value changes |
| fail | Function | No | Callback on failure |
| complete | Function | No | Callback that always executes |
## Success Callback Parameters
| Property | Type | Description |
| ---------------- | ---------- | ---------------------------------------- |
| deviceId | String | Device identifier |
| serviceId | String | Service UUID |
| characteristicId | String | Characteristic UUID |
| value | Hex String | The new hexadecimal characteristic value |
## Code Example
### Basic Usage
```javascript theme={null}
my.onBLECharacteristicValueChange({
success: (res) => {
console.log('Device:', res.deviceId);
console.log('Characteristic:', res.characteristicId);
console.log('Value:', res.value);
}
});
```
### Read and Handle Value
```javascript theme={null}
Page({
onLoad() {
my.onBLECharacteristicValueChange({
success: this.handleValueChange
});
},
handleValueChange(res) {
console.log('Received hex value:', res.value);
this.setData({ latestValue: res.value });
},
readValue() {
my.readBLECharacteristicValue({
deviceId: this.data.deviceId,
serviceId: this.data.serviceId,
characteristicId: this.data.characteristicId,
});
},
onUnload() {
my.offBLECharacteristicValueChange();
}
});
```
### Notify-Based Updates
```javascript theme={null}
// When characteristic has notify enabled, updates arrive automatically
my.onBLECharacteristicValueChange({
success: (res) => {
if (res.characteristicId === '0000FFF1-0000-1000-8000-00805F9B34FB') {
console.log('Sensor data (hex):', res.value);
}
}
});
```
The value is delivered as a hexadecimal string. Parse it according to the characteristic's GATT profile.
## Related APIs
Stop listening for value changes
Trigger a read on a characteristic
Get device characteristics