For detecting a blocker RFID tag, the following steps are conducted. First, a random identifier of a given bit length is created. Alternatively, an identifier is selected out of a probing set, which is stored on a data storage device. The probing set comprises of identifiers, which are not being used as identifiers for a given set of RFID tags. In a second step, a response from all RFID tags is requested having an identifier matching the random identifier or, respectively, the selected identifier. In a third step, it is determined, depending on receiving or not receiving a response, whether the blocker RFID tag is present.