  The ARGO-YBJ experiment has been designed to study the Extensive Air Showers
with an energy threshold lower than that of the existing arrays by exploiting
the high altitude location(4300 m a.s.l. in Tibet, P.R. China) and the full
ground plane coverage. The lower energy limit of the detector (E $\sim$ 1 GeV)
is reached by the scaler mode technique, i.e. recording the counting rate at
fixed time intervals. At these energies, transient signals due to local (e.g.
Forbush Decreases) and cosmological (e.g. Gamma Ray Bursts) phenomena are
expected as a significant variation of the counting rate compared to the
background. In this paper the performance of the ARGO-YBJ detector operating in
scaler mode is described and discussed.

Astrophysics