I know who sent that signal, he's an old "alien" (as you would call him) friend of mine; he does it just for fun while cooking (but he doesn't have a microwave).
I thought Arrival was a very good movie, well worth the time investment. I gave it a score of 8 on IMDb.
I find the director, Denis Villeneuve, to be one of the most interesting current directors. I would also highly recommend Prisoners by him (I gave it a solid 10) and Sicario (which I gave a 9). He's got more movies worth mentioning, but these two could be easy to miss among the better known ones.