One of the main objectives of the CREDO project is to search for so-called
Cosmic-Ray Ensembles (CRE). To confirm the existence of such phenomena a
massive scale observation of even relatively low energy Extensive Air Showers
(EAS) and an analysis of their correlations in time must be performed. To
make such observations possible, an infrastructure of widely spread detectors
connected in a global network should be developed using low-cost devices capa-
ble of collecting data for a long period of time. For each of these detectors or
small detector systems the probability of detection of an EAS has to be deter-
mined. Such information is crucial in the analysis and interpretation of collected
data. The standard approach based on detailed and extensive simulations is not
possible for many such systems, thus a faster method is developed. Knowing the
characteristics of EAS from more general simulations any required probability
is calculated using appropriate parameterization taking into account EAS spec-
trum, energy dependence of particle density and zenith angle dependence. This
allows to estimate expected number of EAS events measured by a set of small
detectors. Results of calculations are compared with first measurements using
a test system. These results can also be useful for the design of more effective
small systems in the future.