There are problems with this situation. As discussed in the previous section, there is the possibility of an indirect effect, with the thermal expansion of the detector causing a polarisation to develop by piezoelectricity. This produces ‘noise’ of a sort, and can mask the signal generated by the target object. There is also the possibility of external stresses being applied. This is a problem, as it means the detector does not work as well as it should. These problems are typically counteracted by the use of a second pyroelectric component, i.e. a reference element.