A new detector capable of measuring the luminosity and beam conditions of the Large Hadron Collider (LHC) is proposed at the interaction point of the LHCb experiment. It will enable real time monitoring of beam parameters, which is of paramount importance in order to safely operate the LHC and its experiments in the beam conditions foreseen for Run 3, starting in 2021, and beyond, towards the High-Luminosity (HL) phase. The detector will provide both online and offline measurements with a feedback at the scale of a fraction of a second, to ensure a luminosity-leveling procedure and a real-time alarm to the LHC.