Why not wear it on the outside?

They would ask you to remove it before entering the scanner.

This is Hacker News, right? :)

Easy solution: stitch it visibly into the fabric of your innermost garment. You want the TSA goons to see the dosimeter if it turns a nice bright mutant-alert color.

I think it would be more effective if it were a nice bright mutant-alert color when you exited the scanner and they asked to see under your shirt because an object was detected. :)