Lately, there has been increasing interest for collecting and analyzing large amounts of data, produced by humans or mobile devices, to generate valuable knowledge. There is a common case where proximity is required between a monitoring device and a mobile target of interest, thus, a Hunter-Prey scenario needs to be implemented. The aim of this letter is to propose a new received signal strength indicator-based tracking technique, based on the Law of Cosines, which can be applied efficiently to the scenario described above. The new algorithm is evaluated through a series of simulation tests and results indicate that it outperforms common techniques such as linear least squares estimators.