optional choice for what? the alarm and immobiliser are there.
basically, there are options that can be set by the installer for things like detecting if a door has not closed properly and you arm it, auto door locking/unlocking, remote boot release, etc. most of these are set at install time as its just a configuration, so you can have them all switched off or on or whatever.
the remote boot and auto power windows require more motors and electronics and more money so i didnt get those intalled. all configurable options are switched on on my car, but its your choice. ask brant to send/fax you the manual. its only a few pages and explains all the options.