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# accessory(_:service:didUpdateValueFor:)

Informs the delegate of a change in value of a characteristic.

```
optional func accessory(_ accessory: HMAccessory, service: HMService, didUpdateValueFor characteristic: HMCharacteristic)
```

## Parameters

`accessory`

The accessory.

`service`

The service with a changed characteristic value.

`characteristic`

The characteristic whose value changed.

## Discussion

This method is called as a result of a change in value initiated by the accessory. Programmatic changes initiated by the app do not result in this method being called.

---

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