The metabolic activity of living organisms results in cellular motion on a nanometric scale that can be efficiently detected by micro- and nano- fabricated sensors. Quartz crystal microbalance and atomic force microscopy (AFM) inspired techniques have recently demonstrated their ability to successfully measure the nanometric motion of microorganisms. Monitoring these fluctuations while exposing the microorganisms to various compounds (e.g., metabolic inhibitors and drugs, fixatives, etc.) provides a rapid, label-free assessment of cellular activity and the live versus dead state of both prokaryotic and eukaryotic cells. To date, microbial activity-induced nanometric oscillations of AFM cantilevers have primarily been measured using commercially available AFMs. In this article we present a novel, user-friendly mechano-sensing device, termed a Nanomotion Detector (NMD), recently developed in our laboratories, that simplifies AFM systems. This NMD offers a streamlined design that is simple to align, is optimized for assays with live cells and liquid exchange, and can be operated in a Peltier-controlled incubator providing thermal control. Here, we successfully tested the ability of the NMD to discern differences between the live/dead nanometric motion of Escherichia coli and Staphlococcus aureus exposed to antibiotics and fixatives. This NMD is a dedicated cell activity detector that can advantageously replace commercially available AFMs for nanomotion detection applications including rapid antibiotic sensitivity testing.