Information leakage in the form of electromagnetic (EM) radiation is an emerging security issue for designers and users of electronic devices. The importance of estimating the propagation area of EM responsible for information leakage is increasing due to the high demand for protecting such devices from eavesdropping. In this paper, we propose an efficient method for estimating the propagation area of EM responsible for information leakage. The proposed idea is to examine the temporal variance of noise in the area of interest in addition to the source intensity and the transfer function. We also show that the information acquired by the proposed method is in close agreement with the actual information acquired in an area of interest by measuring leaked EM radiation.