I have an application where the smartwatch collects some data and send to the phone. I'm using WearableListenerService and GoogleAPIClinet. During the data collection, I want to know when the connection fails. The two functions onConnectionSuspended() and onConnectionFaile() never called even if I turn the bluetooth off. Is there any way to check when the connection drops?
The two functions you mention (onConnectionFailed and onConnectionSuspended) refer to the connection with the Google API client, not with other devices. They'll very rarely get called under normal circumstances.
To detect a change in device connectivity, use the Capability API. Specifically, you want onCapabilityChanged - which, despite the name, gets called when the list of connected, capable nodes has changed, not when capabilities themselves have changed. Documentation is here: https://developer.android.com/training/wearables/apps/standalone-apps.html#detecting-your-app