Today's entry is an interesting one, even if the name is more than a little misleading. This is an issue in the early days of Dungeons and Dragons, and in fact, may other early Role-Playing games in general. These items only work in pairs, and are linked to each other permanently. Anyone wearing one of these may see through the amulet worn by someone else. The description has several parts that are vague, but this only adds to the value!
The possibilities are staggering, with everything from assassins that almost can't be surprised, to voyeur gangs where someone gets the chance to see what only princesses see, or the like. Mechanically, this is not a real game-breaker, but it can have some surprising balance issues with clever players. There is one hard limit listed in the original entry, that each user can only see what is in range of the other's amulet, and no audio or other senses are included. This can really add some spice to an encounter or enemy, so consider the option in your next campaign plan.