I'm a computer programmer. I tested retirement for one year (I called it my "sabbatical") then returned to work for a different company in "level 2" support.
Level 1 support takes emergency phone calls from customers (other companies, not private persons) when they have problems using our programs. Level 2 support is called when the problem is beyond level 1's area, which is mostly how to operate the program.
Our programs are mostly old mainframe "legacy" systems. Most companies update their programs on Sunday when demand for their systems is low. That's when things get screwed up, and Level 1 gets beeped. If the guy/gal in Level 1 is skilled, Level 2 may escape getting beeped. Since I'm fairly new on the product, I'm paired with a skilled Level 1 person, and so far I've only been beeped a few times.