The LQD operator in R-parity-violating supersymmetry can lead to meson decays to light neutralinos and neutralino decays to lighter mesons, with a long lifetime. Since the high-luminosity LHC is expected to accumulate as much as 3/ab of data, several detectors proposed to be built at the LHC may probe unexplored regions in the parameter space, for long-lived neutralinos. We estimate the sensitivity of the recently proposed detectors, CODEX-b, FASER, and MATHUSLA, for detecting such light neutralinos singly produced from D- and B-meson decays in a list of benchmark scenarios, and discuss the advantages and disadvantages of the proposed detectors in this context. We also present our results in a model-independent fashion, which can be applied to any long-lived particle with mass in the GeV regime.