Amulet of ESP
ESP is an abbreviation for Extra-Sensory Perception; that is, perception not gained through the five traditionally-attested senses: hearing, feeling, sight, taste and smell.
This amulet can be identified easily with the far look command. If you notice a monster that you wouldn't ordinarily be able to see (e.g. on the other side of a wall), far look will tell you whether you are seeing it because of telepathy. If so, and you have no other source of extrinsic telepathy, it must be coming from the amulet.
With a chance of an amulet of ESP being generated at 17.5%, this is the most commonly generated amulet, and one of the best: telepathy while non-blind provides excellent early warning of approaching monsters.
- The Eye of the Aethiopica, an artifact amulet of ESP