Digital pregnancy tests have an internal paper test
I'm not too sure why this is supposed to be surprising. When chemical reactions are involved, you often need chemicals.<p>A significant portion of digital meters used for servicing swimming pools require servicing/replacement of strips/chemicals (reagents) within the device.<p>Yes, there are also digital meters that work without chemicals per se, and have special electrodes that measure electric current. However, this approach quite simply doesn't work for all chemical reactions.