Non-Hermitian physics plays a significant role in a wide variety of physical systems, particularly those involving gain and loss, finite lifetimes, or interactions with an external environment. These interactions with the environment often give rise to non-Hermitian behaviour. This Licentiate thesis aims to review some of the intriguing and unconventional properties of non-Hermitian matrices and examine how these properties have been proposed for the development of novel sensor technologies. We present some of the main features of non-Hermitian systems, along with relevant techniques from the theory of open quantum systems—tools essential for modelling quantum sensor setups. In particular, an in-depth discussion of the input-output formalism is provided. Following this, we introduce the basics of estimation theory, a mathematical framework used to evaluate sensor performance. Finally, we review some of the proposals for sensor designs that leverage non-Hermitian effects, as documented in the recent literature.