The infrastructure of communication networks is vulnerable to emergencies or natural catastrophes such as earthquakes, tsunamis, among others. When these emergencies arise, the vast majority of components are affected, hindering communication after the disaster. Both the first organizations to respond (civil defense, fire, and police) and the population in general therefore need an alternative communication system that allows knowing reliable information in real-time. For this reason, in this article, we present a prototype of mission-critical communication using cognitive radio networks (CRN) implemented in software-defined radio devices (SDR), which works on the AM and FM bands. The results show that the cognitive protocol can be implemented in the SDRs and allows the transmission of mission-critical messages in these bands, protecting the integrity of the primary users that are still operating through an energy detector.