In recent years, we have seen tremendous growth in the applications of wireless sensor networks (WSNs) operating in unlicensed spectrum bands. However, there is evidence that existing unlicensed spectrum is becoming overcrowded. On the other hand, with recent advances in cognitive radio (CR) technology, it is possible to apply the dynamic spectrum access (DSA) model in WSNs to get access to less congested spectrum, possibly with better propagation characteristics. In this paper we present a conceptual design of CR-based WSNs, identify the main advantages and challenges of using CR technology, and suggest possible remedies to overcome the challenges. As an illustration, we study the performance of CR-based WSN used for the automation and control applications in residential and commercial premises. Our simulation results compare the performance of a CR-based WSN with a standard ZigBee/802.15.4 WSN.