Remote key fob
 

So I recently bought a 2010 Ford F-150 platinum edition. On the keyremote there's a blue button with a picture of a key on it. I originally thought maybe it came with remote start but when I hold it down it doesn't do anything but beep annoying and give the truck power like it would as soon as you turn it off, take the key out and don't open the doors.

Can anyone please tell me the use of the button?