That's what I thought, too, until I read the Wikipedia article. It turns out there are different kinds of dosimeters:
"Dosimeters measure an individual's or an object's exposure to something in the environment particularly to a hazard inflicting cumulative impact over long periods of time, or over a lifetime. This article concentrates on the radiation dosimeter, which measures exposure to ionizing radiation, but other dosimeters also exist, such as sound dosimeters, ultraviolet dosimeters, and electromagnetic field dosimeters."
The stuff you learn on B&B!
