Use the smartwatch without the phone

Reply to messages without your phone - With your watch

Most watches can receive notifications, with some you can also reply to messages.

Receiving app notifications on the watch is one of the more useful features even when the phone is nearby. Depending on the watch model, you can often reply to messages with pre-set response options that you can edit, such as yes, no, OK, and I can't reply right now, or you can dictate responses that are translated into text. Some watches allow you to type text on a screen keyboard that's too small.

As soon as you leave the pre-set responses, it's often easier to pull out the mobile than to fiddle with the watch, but if the mobile isn't with you, it's of course a different matter. 

Replying to messages without having the mobile with you is probably the feature you have the greatest chance of enjoying if you choose a watch with built-in esim. Unlike most other features that require connectivity, it doesn't particularly negatively affect the watch's battery life, as a message requires a very short time of internet connection.