I have bought myself a smaller device so that I can get on with my writing/editing whilst out and about. This means I will be working on the project on two different devices. How do I (or even, is it actually possible to) sync them, so that when I save on one, the changes are there on the other?
Thanks in advance. 
Yes, is very easy, I use dropbox to save zip backups of project on common dropbox folder between the two machines.
Points to remember.
Hello HSNHnovelist. GoalieDad’s suggestions are similar to the process outlined in this Knowledge Base webpage and are one good way to keep sync data between your two computers.
We also have another Knowledge Base article, which takes the approach of storing your live, working project on a cloud-syncing service and working from that single project on both computers.
The approach you use will depend on how much you trust the cloud-syncing services. Whichever approach you use, making sure that Scrivener on both computers regularly creates its backups will help protect your work.
You might also find this post about backups by kewms helpful as you think about what your backup needs might be.
Thank you for this. I do have dropbox, I should have thought of it but haven’t used it for years. I will need to look at it though as it hasn’t much in it but I keep getting messages saying it is still full and I need to upgrade. 
Thank you. It’s nice to see there is another option if I cannot get my dropbox sorted out. Silly me just thought I could just link the devices through my home wifi. Yes, I’m not young and very out of touch with how technology really works. 
You can move stuff out to create room for the saves, with the free version get I believe is two gigs worth of data.
Thanks. I’ve got it sorted now.
For the sake of giving you all the possible options, if it was already mentioned I missed it, but I personally am reluctant of using cloud services for sync.
I have all my projects on a tiny 64gb thumbdrive. No issues to report yet after quite a good while doing so.
…and I have just as much chances of forgetting the thumbdrive home when I need it, than to leave the stove turned on, or leaving without my wallet or my keys. It quickly becomes part of the involved routine of leaving home.
Thank you. I had thought of that as well, especially since there will be no WiFi where I will be using the new device.
There you go. Decision made easy. 
Here is what I use:
https://www.amazon.ca/gp/product/B07XHYVN62/ref=ppx_yo_dt_b_asin_image_o09_s00?ie=UTF8&psc=1
→ Stay away from the Sandisk equivalent. It is made of plastic, has no aeration holes, and becomes so hot that it melts. lol
. . . . . . .
The idea, should you use a thumbdrive, is to have Scrivener backup your project locally. Not on the thumbdrive itself.
If something bad happens to your thumbdrive, you will still have the backups on those stations.
(Of course, it is recommended to backup those backups – the last one of your writing session – on the cloud (google drive, for e.g.), or somewhere else too.)
Have Scrivener timestamp your zipped backups, and you’ll easily know which one is the most recent, when and if need be.
Work your project from the thumbdrive, do not copy it to the computer you are working on it with, as copies would quickly become confusing, and would lead you to one day discover you actually worked on the wrong version of a project.
Thanks for that. I think I’m going to go with a combination of saving on thumbdrive & Dropbox (when I have a connection)
I will still back up to my home laptop and possibly also on the smaller device.
I’m just going to have to programme myself to always close files and wait for back ups to complete.
To be blunt: I’m not sure that’s a very good idea. It’d be like I said, it is best to avoid project duplicates, as you may very well spend a few hours unknowingly working on the wrong version of your project (the not most recent one).
Say you sometimes use cloud-sync, sometimes a thumbdrive, it is likely that at some point you’ll mistakenly load what you think to be the updated version of your project, confusing the mean by which you intended to carry it over from one place to the other following the previous session.
I’ve never done it. And I won’t. I am not saying it can’t be done right, but it’ll require some system for keeping track, and the discipline to go along with it.
Personally, I’d go with one or the other, but not a combination of both.
Confusion between multiple versions is an extremely common cause of “lost” work. Whenever you create a new copy, please make sure that it is timestamped, has a unique name, or is otherwise easily identifiable. Use that information to make sure that you always know which version you are working on, especially after changing devices.
Yes, I’ve just found the timestamp option for saving back-ups. I intend to be very strict with myself on shut-down and saving routines, or I will get myself completely confused.
The logic outlined here is super sound. Likewise and not unrelatedly, it should also be applied to Scrivener’s own backup functions, so that timestamps are also affixed to the main folder and to the scrivx file inside zipped backups. This would effectively eliminate even the possibility of getting versions and backups confused. As outlined in this thread: Incredibly slow backup when closing Scrivener 3 on Windows 11 - #15 by Mad_Girl_Disease
FWIW, I agree with Vincent here, that a portable drive, in combination with local backups, is a more reliable way to go than messing with cloud services.