Ever simpler. Carol who has the hangover can phone the automated telephone line to clock on from anywhere. Doesn't need Bob's help.
But let's turn this on its head. If there was a fire during cleaning, how would they know who was where? How do you take a headcount at the marshalling point if you don't know who started work, or worse, how many fireman do you commit to a search when Carol hasn't been accounted for?
Miners and plenty other hazardous environments use "clocking" to keep people safe. "I counted them all out and I counted them all back."