Here is one possibility to look into:
I have read in various SHTF books or blogs (can't recall specifically where) that for the average person dosimeter badges or stickers are recommended as an alternative to an instrument type radiation detector.
As I recall, the recommendation is based on the fact that badges are simple, nothing to break, no calibration required and lower cost.
I know that badge dosimiters are available many places on the net - eBay, Amazon, etc. but haven't researched beyond Googling for availability.
Iron, a badge like a Landauer dosimeter badge must be sent in to Landauer for readout. They give the dose you recieved over the previous month.
A pen dosimeter will work, but you need a means to charge them up. A couple of pens and a charger are around $500. Depending on what pen you get, they may saturate in a serious mishap.
They are 40’s tech but I still run into them at almost every rad lab I visit.