[Merlin's explanation is slow, and thorough, and careful - in the way of someone who knows exactly what it's like to be handed a relatively complicated electronic device, having come from somewhere with no greater technology for recording information than quill and paper.]

...people use these to watch for newcomers, I think. There's no announcement that you've arrived beyond any you make for yourself, so - when you're feeling up to it, you ought to.

[God knows he didn't, at first.]