Do take a note that the city is filled with demonic creatures, it'd be hard to sense one demonic precense from another when something lurks around every corner. While not all of them even have a physical body, they can still be very much sensed if person has an ability to sense the demons. Do take a note that not all of them can be seen or attacked, and not all of them are able to attack, a lot of demons around are observers, working as eyes to others. They are there to make sure there is no place to hide.