A transponder detector, comprising: an antenna assembly comprising an antenna coil, a first circuit coupled to said antenna assembly and configured to generate and transmit a detection signal progression via the antenna coil including a high frequency detection signal at a high frequency, a middle frequency detection signal at a middle frequency, and a low frequency detection signal at a low frequency; a second circuit coupled to said antenna assembly, said second circuit being configured to receive a progression of response signals resulting from transmission of the detection signal progression from said antenna assembly, said response signals having an identifying characteristic; and a controller (24, 44) operable to switch the detector between a detection mode and a data transaction mode, the controller being further configured to detect the presence of a transponder having a transponder frequency in a proximal space of said transponder detector based on said identifying characteristic and upon such detection to switch the detector into the data transaction mode, and wherein the controller (22, 44) is further configured to evaluate a power level of the received progression of response signals and to assert a protection mechanism to protect the second circuit from the incoming energy when an unsafe threshold level is exceeded; wherein said first circuit comprises a first switched series resistor, a first resistance switch, a second switched series resistor, and a second resistance switch, and further comprises a first switched parallel capacitor, a first capacitance switch, a second parallel capacitor, and a second capacitance switch, and wherein said detection progression signal is generated by cooperatively controlling positions of said first and second resistance and capacitance switches (66,70,76,80). an antenna assembly comprising an antenna coil, a first circuit coupled to said antenna assembly and configured to generate and transmit a detection signal progression via the antenna coil including a high frequency detection signal at a high frequency, a middle frequency detection signal at a middle frequency, and a low frequency detection signal at a low frequency; a second circuit coupled to said antenna assembly, said second circuit being configured to receive a progression of response signals resulting from transmission of the detection signal progression from said antenna assembly, said response signals having an identifying characteristic; and a controller (24, 44) operable to switch the detector between a detection mode and a data transaction mode, the controller being further configured to detect the presence of a transponder having a transponder frequency in a proximal space of said transponder detector based on said identifying characteristic and upon such detection to switch the detector into the data transaction mode, and wherein the controller (22, 44) is further configured to evaluate a power level of the received progression of response signals and to assert a protection mechanism to protect the second circuit from the incoming energy when an unsafe threshold level is exceeded; wherein said first circuit comprises a first switched series resistor, a first resistance switch, a second switched series resistor, and a second resistance switch, and further comprises a first switched parallel capacitor, a first capacitance switch, a second parallel capacitor, and a second capacitance switch, and wherein said detection progression signal is generated by cooperatively controlling positions of said first and second resistance and capacitance switches (66,70,76,80).