surf key

when I bought my van I was given 3 keys. 2 of them are the remote key fobs that work as expected. I also received a ‘normal’ key. Non folding no big fob. What is the point of this key? If I open the door with this key the alarm goes off.

Does anybody know if: On my T5.1 I am able to lock the vehicle manually using an unchipped key and then a couple of hours later unlock the vehicle without setting off the alarm. That allows me to take the unchipped key sailing without the risk of getting the electronics in the standard key...