  In this paper we report test results from a prototype designed to detect
muons from horizontal air shower at large zenith angle,
  $86^{0}<\Theta<93^{0}$. To detect horizontal tracks and their directions we
select them according the muon vertical equivalent charge and we measure the
time of flight with a time resolution of 800 ps. Several measurements are
collected at different zenith angles. The background studies performed with two
modules show that the main source is due to tracks crossing the module at the
same time. The upper limit of background flux for a single twin module is
estimated to be $10^{-9} cm^{-2}$ $s^{-1}$ $sr^{-1} (90%CL)$. We estimated the
size of the surface array necessary to detect the shower flux of the order of
$10^{-9} cm^{-2}$ $yr^{-1}$ $sr^{-1}$ if originated by Tau Air-Showers
secondaries of GZK neutrino Tau below the horizons.
