It is inter-alia disclosed a method comprises:



obtaining or holding available at least one training set of radio signal observation results, wherein a respective training set of radio signal observation results is held available in association with identification information of a corresponding area of interest on a site, wherein a respective training set of radio signal observation results is captured at a corresponding observation position within a corresponding area of interest on said site;
obtaining or holding available area of interest information indicating whether at least one tracking device has been determined to have entered and/or to have been located within a corresponding area of interest on the site;
obtaining or holding available current radio signal observation data of a current tracking device representing one or more current sets of radio signal observation results captured by a radio interface of the current tracking device when present on said site, wherein a respective current set of radio signal observation results is captured at a corresponding observation position on said site;
determining whether the current tracking device has entered or is located within an area of interest, identification information of which is associated with the at least one training set of radio signal observation results, based on at least one current set of radio signal observation results, based on at least one training set of radio signal observation results associated with the identification information of the area of interest, and based on the area of interest information.