The scale of the COVID-19 pandemic has highlighted an urgent need for versatile diagnostic strategies. To address this need, we sought inspiration from the previously described toehold RNA switches and engineered RNA-based biosensors that directly detect SARS-CoV-2 RNA. In our assay, a fragment of SARS-CoV-2 RNA binds and activates the biosensor, leading to a conformational switch in the RNA sensor. This then leads to translation of a reporter-protein e.g. LacZ or Nano-lantern that is easily detected using color/luminescence. To increase sensitivity of detection, we coupled the assay with an initial step of isothermal RNA amplification. By optimizing RNA-amplification as well as biosensor-design, we have generated a highly-sensitive diagnostic assay; with sensitivity down to a 100 copies of SARS-CoV-2-RNA. The color response can be visualized by the human eye, or a simple cell phone camera, where as in the luminescence mode the response can be quantifed using a luminometer. We find that our biosensor efficiently detects the presence of viral RNA in human patient (naso-pharyngeal) samples, and this response correlates well with Ct values from standard RT-qPCR tests. Thus, we offer a SARS-CoV-2 detection platform that does not require any sophisticated equipment and is usable even in a low resource setting. The pipeline we have set up can be easily used for other viral diagnostics in future.