An aspect of this invention is a portable caffeine detector, which is optionally called The De-Caf Stick. It is a test strip that is inexpensive, is safe and easy to use, may be carried in a pocket, briefcase, computer case, handbag or the hand and can be used to determine the presence or absence of caffeine in both hot and cold beverages before they are consumed. The caffeine detector is disposable and, preferentially, is made of biodegradable polymeric materials. The results of the tests can be detected calorimetrically, without the use of instrumentation or reagents. Another aspect of the invention is a carrying case for holding a plurality of the test strips. A further aspect of the invention is a method of detecting caffeine in a beverage using the portable test strips.