On iOS devices, calls made through DuoxMe are integrated with the iPhone's Phone app. At the moment, Apple does not offer support for these calls to be mirrored on the Apple Watch (they work in the same way as WhatsApp calls, which also do not reach the Apple Watch).
On Android devices, the DuoxMe app calls work through push notifications, so as long as your smartwatch allows you to duplicate the notifications from your mobile, you will be able to receive the call notification on it, as well as the "Call already answered" or "Missed call" notifications.
To answer the call or open the door you will have to do it from your mobile/tablet, as we do not have a version of the app for smartwatch at the moment.