Hi, I just noticed it in my phone. After a little researching on the internet, I have found that it is mainly used for Samsung flip cover cases to detect when it's closed and display the suitable AOD. Perhaps it also detects on body detection but I am not sure. It uses a kind of electromagnetic field to sense the presence of palm on the backside of the phone much like the Spen technology. Some people are also saying that it can detect how you are holding your phone and then turn off those antennas that are covered by your palm to save battery.
Here, I am giving the link to its patent.
If you know any more details about this sensor and how it works, plz share. Would love to read.
Update: I just found it shows 'working' if you bring your hand near the bottom of your phone. It basically assumes that you will be holding your phone towards the bottom and that way it senses. It is not a pressure sensor since it needs touch. It is an inductive sensor since it can detect presence of hand even while not touching the phone.
Don't believe me? Hold your phone by the top, it will think you are not holding your phone.
