This paper aims at investigating the relationship between the notions of indiscernibility, threshold and medium at the beginning of Homo sacer, in particular in the two first volumes of Agamben’s project: Homo sacer. Sovereign power and bare life (Homo sacer, I, 1995), and State of Exception (Homo sacer, II, 1, 2003). I intend to show how the nexus, as well as the gap, between these two books, consists in the declination of Agamben’s reflection on the topos of indiscernibility into a thought of the «threshold», or «medium». I contend that this move leads the author, in State of Exception, to introduce the concept of «use» in the medial sense that it assumes in the development of Homo sacer project. Through an analysis of two subsequent texts of the author, the essay Philosophical archaeology (included in The signature of all Things, 2008), and The Use of bodies (2014), I show how the notion of «use», inasmuch at it consists in the pivotal point of power’s apparatuses, and at the same time of their opening into a «new use», stands as the basis of the «archaeological method» of Homo Sacer project, which Agamben develops in a soteriological key.