The MOGLabs MGSA is a compact atomic reference for stabilising tunable lasers. It uses saturated absorption spectroscopy with an alkali cell (Rb, Cs or K) to provide an absolute frequency reference. Beam expansion reduces power broadening so that spectral features approach the natural linewidth. The laser can be PM fibre-coupled or free-space. A low-noise amplified photodetector is included, with connection compatible with the MOGLabs DLC range of laser controllers. A resonant Zeeman coil allows modulation for AC locking, without modulation of the laser itself.