We propose a novel concept of metamaterials, based on a smart, programmable unit cell. This new metamaterial is presently used to devise new nonreciprocal devices in acoustics, illustrated by the design of an acoustic diode, or isolator. A boundary control strategy was previously shown to provide direction-dependent propagation properties in acoustic waveguides. In this paper, the boundary control is reinterpreted as a source term for the inhomogeneous wave equation, in a purely 1D model. Nonreciprocity is then obtained using a distributed source that replaces the non-standard boundary condition where the normal velocity at the boundary is a function of both pressure and its tangential derivative. Numerical simulations are carried out to validate the theoretical model, and the scattering matrix of the device is retrieved to investigate the nonreciprocal nature of the system. Finally, an experimental validation is carried out and transmission measurements are presented. Results show that the proposed smart metamaterials is able to realize an efficient, ultra-broadband, sub-wavelength, acoustic isolator.