It would surprise you to know that most professors don’t even know if you’re showing up for class.
There is no checklist, nobody is reading out an attendance card, it’s not any kind of requirement on your part. You’re paying for it, anyhow. If you want to use the service you’re paying for, that’s ultimately up to you.
In my third year of mathematics, I was in upper division Linear Algebra with Ken Ribet. It’s normal to be taught by top notch mathematicians at Berkeley.
That class had about 100–200 students in it. It’s likely that this wasn’t the only class that Ribet taught.
It wasn’t a room. The place looked like this.
I’m fairly certain this is a picture of the exact auditorium the class was taught in. The only person that anybody recognized when absent was a student who I regarded as a genius. This student would consistently correct Ribet on his board. Ribet is a world-renowned mathematician, credited for paving the way towards Andrew Wile’s proof of Fermat’s last theorem. If this student was missing, anybody would know. The room would be quiet and the faces would all look the same. For the most part, the students in these classes were studious, quiet, and hard workers. They didn’t ask questions and mainly listened in on the lectures.
In fact, anybody could simply walk in and audit the classes. On several occasions, I would notice people around 50–60 years old who were not students sitting in and taking notes.
The professors didn’t care. If you were there to learn, awesome. If you were there to ask questions or correct mistakes, awesome. If you didn’t want to attend, the curve is stated on the syllabus and your grade is composed of one-half midterm and one-half final.
This was the upper division course, too. There was a differential equations course, the last course you take in your lower division line-up. That course had something like 500 students in it. If you didn’t show up the entire semester, nobody would know. The only important thing for those classes was that your student ID was on the midterm, homework, and final.
One addendum: For most courses with a lot of students, the class gets split up into additional discussion sections. These are additional classes you take with the teacher’s assistants, or graduate students, who teach you the material in depth. These classes tend to be smaller and far more helpful than any lecture. If you didn’t attend one of those, the TA would probably notice. In fact, I would argue that it is absolutely essential to attend your discussion sections while the lecture could be viewed as supplemental. I hold this view because Berkeley, like any elite college, has a lot of professors that are busy with research or out doing activities you would expect out of a Nobel laureate. It’s not uncommon for a professor to backseat their students while pursuing research.