Not sure what the other commenters mean with "HN is not the place for this". He is asking about an idea, he is not testing anything.

As for the app, and also as someone who loves tracking himself, I would like it. In fact, I did this manually in my google calendar at one point but only for a month or so because there was too much friction.

I am also interested in how it would detect being with someone. Seems strange. Another solution, which I am using in a personal tracking project, could be to simply send a local notification at the end of each day - asking "Who were you with today?". I've noticed that this works pretty well. I send one to myself once after 24 hours, and then twice (+24more) if the first one was not "answered".