The instadose™ dosimeter from Mirion Technologies offers a small radiation dosimeter with a monthly subscription charge. It's a nice device, but instead of selling you the device they force you to use their monthly subscription service. I believe that the technology is so simple and cheap that they can't make enough profit just by selling the device to you.
The Mircon Technologies Instadose dosimeter badge uses what Instadose calls direct ion storage technology. The badge has a USB interface. Sadly, it uses some proprietary interface that requires a special driver that works only under Windows.
I suspect it's a fancy electrometer with a FET detector to read the charge. The device contains a couple of lithium button cells, a microcontroller, and a "mysterious box", which I assume is the detector.