A swallowable in-vivo device comprising a shell defining a cavity of the in-vivo device, the shell being formed with at least one aperture extending through the shell's wall. The in-vivo device is configured for allowing inlet of fluid into the cavity; The in in-vivo device further comprises and immunoassay system accommodated within the cavity and configured for interacting within the fluid; The in-vivo device also comprises at least one breach mechanism covering the at least one inlet for preventing ingress of fluids into the cavity via the inlet; The at least one breach mechanism comprises a film layer configured for reacting with the fluid and designed to be breached after a predetermined amount of exposure time to the GI fluid, corresponding to a desired location along the GI tract.