At the high school, there 3 deep fat fryers that sit on the floor. And each one has two arms on the top that lower and lift the baskets from the oil, which are controlled by digital timers. When the time is up it beeps and lifts the baskets by itself. Yet, I seen fryers at McDonald's that only beep but the cook have to lower or lift the baskets from oil. Why do some fryers have this and some not. I figured McDonald's or other fast food would because of how many french fries they cook all the time, but they don't have it.

Plus at the junior high they had one fryer and it too had the arms and timers. So it seems like most schools use these fryers instead of the manual ones.

However, I never seen a household type fryer with such a device on it.

It is an add-on thing, you choose if you want it or not.

It is to some extend a food safety thing: The automated lift mechanism prevents the food to become overdone (when the cook delays somewhere and let it fry longer) and so develop too much of the nasty chemicals the overheat tend to make.

Plus it saves a bit on labor, when there are just few cooks for a large canteen: The fryers do not need that much attention, so the staff may do something else during the frying time.

And why McDonald dont use that? It costsmoney and the food safety is their concern only up to passing really the minimum legal requirements.
Plus the routine there allows them to have an employee busy solely to operate the fryer, so not much saving from there...