Call notification?

Any, all or combination of these can be enabled for incoming call if watch is paired with a phone and there's a Bluetooth connection between them.

Simply show notification and/or vibration and/or beep sound.

yeah because was strange is only one beep and vibrating thinked maybe more little fancy sit inside :D (i mean beep song)

One thing to be aware of with phone call notifications on Android phones, is you should disable the "Phone" app notifications in the Smart Notifications settings in the Connect app.

The reason is because the Connect app will send a call notification to the watch regardless of whether the "Phone" app notifications are turned on, but if you do have the "Phone" app turned on then it will end up sending two phone call notifications to the watch simultaneously and confuse the watch, often causing it to display neither of them.

Whenever someone has issues with the watch only displaying phone call notifications "sometimes", that's usually the reason.