Systems and methods are described for detecting the presence and/or absence of a solid, liquid or gas which utilize an RF energy emitter and RF energy detector for determining whether a solid, liquid or gas is present within a defined physical space. More specifically, an RF energy emitter is provided at a first side of a solid, liquid or gas transmission channel and an RF energy receiver/detector is provided at an opposite side of the solid liquid or gas fluid channel. The RF energy emitter either continuously or periodically emits RF energy which in the preferred exemplary embodiment is in the high-frequency or more preferably ultrahigh frequency signal range. The amount of detected RF energy transferred across the channel is used in determining the presence and/or absence of a solid, liquid or gas.