How will "they" know we're on a different/new device?

Question

Web development

I mean backup, restore on new hardware and some sites understand that I'm on a new device, and some do not

, what does it depend on, what should I do so that the transfer is completely without problems?

Answer 1

It is worth reading about browser fingerprint.
By the way, there are addons for constantly changing the fingerprint identifier...
PS And there are also cookies and localStorage, honestly!

Answer 2

Briefly:
There is a server "there" and feeds your browser / system fingerprints, etc. neural network, which is trained to determine the correspondence - that's it.
Long:
It really depends a lot on who "THEY" is, what kind of system \ IP \ MAC \ hardware ID \ SOFT and whether the software on the IM device belongs (well, at least one softinochka ala "clock", "music", social network or "live wallpaper"). Those. there is no difference who/what and on what device, if the office made the site and the device or the site and at least one software on the device (browser). Either the site cooperates with the office in terms of user identification. Even without any miscalculation, on a clean system there is a "pattern of behavior on the network", "mouse movement features", all this is unique, being available at least a couple of factors (just went to "their" sites) - you will be recognized . They entered as a specific person - they recognize it as a specific person.
Advice:
A virtual machine with the right OS, each time new, with a new IP + simulation of a different style of behavior of the average on the network, at least for 10-15 minutes + no software left (even from other manufacturers).
Good luck!