Stereo head unit replacement

[CA_Boxster]

I'm replacing the stock head unit with an Alpine and was told buy a guy at Best Buy that their system says I need an anti-theft bypass adapter (Directed Electronics 555U: http://www.caraudio-caralarms.com/555U.html). I can't figure out why I would need this thing and am assuming that what they really mean is that I need a wiring adapter (Crutchfield recommends one) to make the install cleaner. Has anyone run into this before? Any info will be appreciated. It's a 2000 Boxster with the door speaker option.

Thanks.