Create user to monitor database activity on Postgres Postgres 9.3
Debian 7

I want to create a monitor user called monitor that the only permission is to run queries to monitor all the database activity.
I created the user and it can select from pg_stat_activity, the problem is that it only sees it's own activity and I want this user to see all users activity.

Is there any special privilege to do that?
At this time, only superusers can see others' activity details in pg_stat_activity.

PostgreSQL could use a finer-grained rights model, where you can GRANT the MONITOR_QUERIES right to a user, for example. But right now it doesn't have one, and quite a few things are superuser-only. This is one of them.