A few weeks ago, Lumia 930 and 830 units started receiving a firmware fix for 'periodic reboots', but it seems that this is, in fact, a platform-wide phenomenon, since the AAWP device stable has lit up this morning with the same update now available on the Lumia 1520, 1020, 920, 625, 530, and a few others besides... The new (fairly small) update takes Windows Phone OS to v8.10.14226.xxx (in the 1020's case), but shouldn't be confused with Windows Phone 8.1 Update 2, which may well come to devices other than the 830 and 735 in some regions. I'll report more on that in due course.
As usual, check for 'phone update' in Settings - and make sure you have your device fully charged up or plugged into a charger, just in case.
The new update take only a minute to download and only about two minutes to install, which is fast by Windows Phone standards.
As the screen suggests, the idea is to fix a bug in the OS whereby the phone 'randomly' reboots every now and then. Personally, I haven't seen this on any of my Windows Phones, but in fairness, they're rarely on for more than a week or so - there's always some reason why I need to power down (e.g. to change a SIM)!
Comments welcome if you've seen this small update on other Windows Phones.