Ah SQUIRREL! attacks again Zaromas; I was too one-track minded to see your original post. Not quite how things function. Right-clicking the forcefield itself with a multitool set to the correct setting will allow/deny entry for those with permissions. ID cards are used in conjunction with the security station to set permissions on a per-user basis (aside from the creator of said forcefield setup of course).
The external ID reader I believe (the rest of this is speculation as I don't play on any servers) functions in that someone who wishes some sort of access can pass their ID card that they made to some attached storage without exposing the storage block to the outside world. i.e. placing the ID reader outside the forcefield setup.
However, looking at 184.108.40.206.17c (the latest as of this post) that external ID reader no longer exists in NEI.