The GSM standard is a regular signal in the time domain with a TDMA frame of 4.615ms divided in 8 time slot of 577ms. Then from a CW calibration and a mean value measurement with a high sensitivity multimeter, it is possible to measure the SAR (Specific Absorption Ratio). Now, with the new standard, like WIFI 802.11, b,g,n , WIMAX, LTE, the signal in the time domain is irregular with random effect. Then a temporal measurement is required and the response time should be consistent with temporal specification of these new standards. Due to the high input impedance of the SAR probe, not only the probe contributes to the time response but all the acquisition system including the probe, cable, data acquisition module. Firstly, a test bench for the response time measurement is presented. Secondly, the simulation of the total acquisition system allows predicting the performance of the SAR measurement system according to the type and length of cable, the specification of the data acquisition module (Input impedance, capacity). Finally, the interest to implement a matching circuit near the probe is presented.