Default source of driver activity is iButton. To set another activity source, use the command unit/update_activity_settings

svc=unit/update_activity_settings&params={"itemId":<long>,
					  "type":<int>}

{ } /* success execution */

Parameter “type” values:

To get the selected source, use the command unit/get_activity_settings

svc=unit/get_activity_settings&params={"itemId":<long>}

{
"type": <int>		/* selected source */ 
}