Spoiler: I had trouble with the third object too, but I figured how it was used once I noticed the "Radar" name: you click once to activate it, and then, it will make noises and rotate depending on whether you are close to a Shapeshifter or not. This is precisely a counterexample to the preciousness/scarcity of the two other items, since it does apparently recharge infinitely, which I thought was a problem as it can make the game too easy, but I agree that scarcity for the rest is a good idea!