Hardware Trojans are an emerging threat that intrudes in the design and manufacturing cycle of the chips and has gained much attention lately due to the severity of the problems it draws to the chip supply chain. Hardware Typically, hardware Trojans are not detected during the usual manufacturing testing due to the fact that they are activated as an effect of a rare event. A class of published HTs are based on the geometrical characteristics of the circuit and claim to be undetectable, in the sense that their activation cannot be detected. In this work we study the effect of continuously monitoring the inputs of the module under test with respect to the detection of HTs possibly inserted in the module, either in the design or the manufacturing stage.