This document proposes an Exponential-Rayleigh (ER) model for device-free localization and tracking using wireless sensor networks. The ER model accounts for both the large-scale exponential attenuation of signals and the small-scale enhancement of signals from target-induced multipath components modeled by a Rayleigh distribution. Experimental results show the ER model outperforms existing models by mitigating multipath interference effects and improving localization and tracking performance.