Described is a reader device for contactless reading of transponder data via an electromagnetic field having a read antenna connected to a receiving circuit for demodulation and preparation of transponder data.The reader device includes a digital signal processor that is connected to or forms part of the receiving circuit for generating a display signal showing an amplitude-time curve and/or a frequency spectrum of the received signals. The display signal travels via a display signal output of the digital signal processor to an optical display device integrated in the reader device or via an integrated interface to an external optical display device.