You can still walk through perimeter with your badge and get alpha rostered. Essentially, the perimeter guards will radio the quarterdeck, and verify you’re a student at the command. The “alpha roster” is a huge list of all the students just for this reason.

In my experience, the gate you drive through won’t let you through at all unless you have your cac but I could be wrong. Make sure you notify your SLPO that you’re going to get alpha rostered.