International audienceThis paper presents an evolution in an optimization method, called FlexIn, developed for the optimal design of piezoelectric compliant smart structures. FlexIn is based on a flexible building block method that uses a genetic algorithm approach, to optimize a truss-like planar structure made of piezoelectric passive, active and, with the work reported in this paper, sensitive building blocks. The model of these blocks is established by means of a finite-element electromechanical formulation. The main contribution of this paper is to present a new observation-oriented criterion, along with a static electromechanical one, considered in the optimization procedure for the optimal placement of piezoactuating and piezosensing parts in the compliant micro-structure. In order to underline the interests of such a criterion, performances of three pseudo-optimal piezoelectric smart structures are drawn. Their analysis and comparison illustrate the role of the optimization method and the observation-oriented criterion, in the design of smart structures and in simplifying their control afterwards