How to get the Lifeform Analyzer

The Lifeform Analyzer is an informational accesory that displays the name of rare enemies, critters, and undiscovered NPCs within 81,25 tiles around the player. It is purchased from the Traveling Merchant for 5 gold coins! It is one of the three parts necessary to make the R.E.K. 3000, with the others being the Tally Counter and the Radar, and as such is required ingredient in making the Cell Phone!

It's not that hard lol