An increasing number of studies in cognitive science make use of introspective responses. With the notable exception of confidence judgments, most of these responses are used as valid markers of subjective states, while their generative mechanisms are left unexplored. Here, drawing on two set of studies, I will make the case that the general framework of signal detection theory applies to introspections, as it applies to perceptions. First, I will present behavioral and pupillometric data from mind-wandering experiments suggesting that when participants are asked to report whether they are on-task or mind-wandering, they do so by comparing the level of an internal state variable with an adjustable criterion. Mental monitoring of mind-wandering thus exhibits a fundamental signature of signal detection. Second, I will focus on self-estimation of response times, as a specific case of self-observation. While it is known that participants can, with some limitations, report the speed of their own decisions, we don't know how this is achieved. Here, by means of bayesian modeling of response times, I will show that the psychometric properties of these second order decisions are similar to those of first order decisions. Together, these findings converge on the notion that mental monitoring and self-observation can be modeled as inner or second order decisions. I will discuss the implications with respect to the functional significance of introspection.