Some people drink decaf coffee. These people, given normal coffee, will go apeshit, bouncing off the walls and breaking things. Given espresso, they will spontaneously human combust and create a black (coffee) hole that will smell like fresh roasted beans and suck many an oblivious barista into its odoriferous depths. That's why it's important they never drink regular coffee or a Red Bull. To keep the rest of the world safe from these people, somebody developed D+Caf strips.
D+caf test strips are simply little strips of paper coated with antibodies that tell if you a beverage is properly decaffeinated, turning up blue lines if it's got more than 20mg of caffeine per 6oz serving. Even modern decaffeination procedures can't remove every single trace of caffeine, but between 20 and 30 percent of coffee and tea drinks "contain unacceptably high levels of caffeine" according to the strip's maker, Silver Lakes Research.
A box of 20 strips costs $10 and I really wish they were Roof+e strips instead because the Superficial Writer keeps eyeing me salaciously and encouraging me to chug my Appletini.