A device (1) for monitoring a response of a subject body (2, 21, 211) comprises an emitter (3) for emitting an input signal (5, 51, . . . ) and a receiver (4) for receiving an output signal (6, 61, . . . ). A first response (R1) of the subject body (2, 21, 211) is evaluated from the comparison between the signals. A further emitter (31, 311, . . . ) evaluates a second response (R2), wherein one of the responses is selected for a further monitoring of the response, and/or at least one further receiver (41, 411, . . . ) evaluates a third response (R3), wherein either the first response (R1) or the third response (R3) is selected for a further monitoring of the response, and/or wherein the input signal (5, 51, . . . ) is an electromagnetic field and the device (1) further comprises a signal modulator (9) which alters the input signal (5, 51, . . . ).
