The classical instability strip harbours a plethora of variable stars, such as the well-known dsct, gdors and roAp stars. Only recently another class of oscillators was found very close to the main sequence of the classical instability strip, the pre-Extremely Low Mass White Dwarf (pre-ELM WD). With masses bellow 0.3 Msun, pre-ELM WD have He-cores resulting from mass transfer in binary systems at the Red Giant branch . Although delta Scuti stars are usually found near and on the main sequence and pre-ELM WD are usually located just before the terminal white dwarf cooling sequence, the two groups share a common range of excited pulsation periods and have very similar atmospheric characteristics which can result in misclassification. In this talk I will give an overview over the characteristics of both groups and present asteroseismic tools which allow us to distinguish between the different evolutionary stages without the knowledge of the stellar mass and clear mode-identification. This work will allow us to address open questions related evolution and stellar structure of pre-ELM WDs. In addition, the upcoming TESS mission will provide excellent photometric observations of a significant number of objects in this particular region of the HR diagram, increasing the need for a correct classification.