I've read, too, that Russia did some nuclear simulation, and that now US is moving nuclear rockets to Finland, so yeah, I understand your concern.
Beware that selling, and in some parts of the worlds even owning a radiation detector without a permit might be forbidden by local laws. Some years ago we use to have a guy, here in Ro, that developed a detector and made an application for a google map global radiation network, his nickname "radue". This is the first link from rsearch
https://www.pocketmagic.net/global-radiation-monitoring-network/but I remember he used to have for sale radiation detectors that can be connected to LAN and continuously monitor the environment, outside or indoors. His business took flight by the time of the Fukushima events.
No idea if he's still selling, probably yes.
Beware many of the detectors are for catastrophic events only, and not very sensitive. There is also a big difference between radiation detector and personal dosimeters. One can stand to high radiation levels for a short time, but for measuring health damage/safety, then you'll need a dosimeter.
Let's hope we will never need any of those, after all the war is always very profitable for the very rich and very powerful. My best guess they won't want it ended too soon. So unless nukes or related false flags will be used as a pretext to start a WW3 (I hope this will never happen, since now the idea is common knowledge) then you'll probably never need a radiation detector.