The performance of networks for indoor localization based on RF power measurements from active or passive devices is evaluated in terms of the accuracy, complexity, and costs. In the active device case, the terminal to be located measures the power transmitted by some devices inside its coverage area. To determine the terminal position in the area, power measurements are then compared with the data stored in an RF map of the area. A network architecture for localization based on passive devices is presented. Its operations are based on the measure of the power retransmitted from local devices interrogated by the terminal and on their identities. Performance of the two schemes is compared in terms of the probability of localization error as a function of the number (density) of active or passive devices. Analysis is carried out through simulation in a typical office-like environment whose propagation characteristics have been characterized experimentally. Considerations obtained in this work can be easily adapted to other scenarios. The procedure used for the analysis is general and can be easily extended to other situations.