This paper attempts to discuss the "new alienation" in the posthuman condition. We refer to the "new alienation" as the situation in which our self-knowledge was affected by the power of the algorithmic regime. We use digital self-tracking practices as examples, which include the quantified self movement and self-care in digital health. Both are practices enacted by the assemblage of "users - digital self-tracking devices - algorithms - databases". Past research usually focused on the governance and the self-discipline of the self-tracking practices under Michel Foucault’s theoretical frame of "biopolitics". Different from them, this paper argues that we are living in the algorithmic regime in this datafied world. The exercise of power diffuses across daily activities assembled by various kinds of information technologies, wearable devices, sensors, and algorithms. The heterogeneous (human and nonhuman) actors are assembled to affect and be affected by each other. It is also in this algorithmic regime that the self-tracking practice users are "dividualized" and become "data selves". We then argue that the "new alienation" is highlighted in these daily using experiences. It is a kind of experience of disjuncture when a user tries to "know himself/herself". In other words, we call this condition the "interpolation" of subjects. The data selves as dividualized and assembled identities are open to continual revision and becoming which is in some way affected by the operation of various kinds of algorithms.