APCO Project 25 (P25) is the digital communications standard that has widespread deployment amongst emergency first-responders in several different countries. This paper describes the implementation of a low-cost software-defined radio receiver for APCO Project 25 signals. The OP25 Receiver has been developed as part of an investigation into the security of the P25 protocol suite and provides low-level access to the actual message traffic using the WireShark packet sniffer. The proposed OP25 Receiver is a useful diagnostic and security analysis tool. Our initial experience suggests that the flexibility of the software-defined radio approach is well-suited to meeting the varying needs of public-safety radio communications.