Abstract: Fraudulent toll telephone calls are detected by the recognition of extraneous supervisory signals which are generated in the originating office in response to a perpetrator placing such a call. The invention provides a means of detecting a second proceed-to-send signal received at the originating office and of recording in memory means the identities of the calling and called parties. Timing means for achieving the detection is connected to the automatic message accounting trunk circuit of the originating office and, upon detection, an MF receiver is also connected thereto for a predetermined interval of time.