Comparing the mean features of helium proportional counters with the ones of the standard boron trifluoride tubes, it appears at glance that, in equal term of efficiency and for the same active length, the 3He filled counters are characterized by a very smaller diameter which optimizes their spectral resolution and minimizes wall effects. Moreover helium counters are usually designed in standard diameters and the 2 inch size is commonly available in a wide set of sensitive lengths. This manufacturing characteristic suggested us the realization of a modular neutron detector with a variable geometry to be adapted to counters of different lengths. At first a small modular detector (length of 80 cm) was assembled in Rome at SVIRCO Observatory and TPL during 2006. In March 2010 a second larger modular neutron monitor (length of 216 cm) was realized as well to be used for cosmic ray registration with a higher counting rate and better reliability. A short description of both modular cosmic-ray detectors is given.