A device, for signaling a presence of animals inside monitoring units for locating animals, of a type having a box body configured to contain animals and provided with at least two access ports and respective mechanical mechanism for opening and closing the access ports. The device includes a detecting and signaling device of the presence of at least one animal inside the box body. The detection and signaling device can be activated to open and close by a switch element (103) which can be associated internally to the box body and which can be shaped in such a way as to be activated by a plurality of mechanical mechanisms that are mobile with respect to the box body and located internally thereof.
