  A luminosity monitor, based on plastic scintillator detectors, has been
developed for the SIDDHARTA-2 experiment aiming to perform high precision
measurements of kaonic atoms and was installed in 2020 on the DAFNE $e^+e^-$
collider at LNF (Laboratori Nazionali di Frascati, INFN). The main goal of this
system is to provide the~instantaneous and integrated luminosity of the DAFNE
facility by measuring the rate of $K^+K^-$ correlated pairs emitted by the phi
meson decay. This task requires an accurate timing of the DAQ signals, as well
as timing resolution below 1ns, in order to disentangle the $K^\pm$ signals
from the background minimum ionizing particles (MIPs) produced during the
$e^+e^-$ collisions at DAFNE. In this paper the luminosity monitor concept as
well as its laboratory characterization and the first results inside DAFNE are
presented.
