We discuss the characteristics of new sensing elements based on a symmetrical metal-semiconductor-metal structure, which are designed for detection of microwave-terahertz signals. The schemes of connection of the sensing elements in the high-frequency path and the low-frequency measuring circuit are considered. Expressions for the volt-watt sensitivity and the noise-equivalent power are obtained. Comparison of the obtained characteristics with those of the detector zero-bias Schottky (Mott)-barrier diode is carried out. It is shown that the characteristics of the symmetrical sensing elements are comparable with or exceed in some cases similar characteristics of the detector zero-bias diodes.