Obsolescent two-in-one device

As a detective, my first step in solving the mystery of the crossword clue ‘Obsolescent two-in-one device’ was to break it down into its key components. The clue indicated that we were looking for a device that was no longer commonly used, and that this device served two functions. My first thought was that it might refer to the once-popular devices that combined a pager with a phone, or a PDA with a phone. However, ‘obsolescent’ implies that the device is no longer used today, and these combined devices are still found in modern iterations.

Then, I considered the ‘two-in-one’ aspect of the clue. Perhaps it was referring to a device that combined two functions in a more literal way, such as a watch that also functioned as a calculator. This led me to a new line of thinking that eventually brought me to the answer: CALCULATOR WATCH. These devices were wildly popular in the 1980s and early 1990s, but have since fallen out of use in the general population. Through deduction and close examination of the clues, I was able to successfully solve the mystery of the crossword clue and reveal the forgotten device that was being referenced.