In U.S. cars pre 2009 (forget which date) the wiring is all there.
When you retrofit the alarm -> the siren goes in the shell well, the interior motion goes in the dome lights, and a switch under the hood.
After that, you still need coding but some basic things function.
Most notably, the clown nose starts to blink when the doors are locked.
I just did the install and had my car coded.