The ItemFinder wasn't perfect at finding items in the original releases of Pokemon Red and Green.
You're probably familiar with the hidden items that are scattered throughout the various Pokemon games. There seems to be nothing on the ground, but if you press the A button, you'll find a (generally pretty good) item. Collecting a hidden item in Celadon City [https://rgmechex.com/articles/2023-03-05/img/hiddenitem.gif] A lot of these items are kinda obvious like this one, but some aren't so easy to find.