The MX651 is a low power integrated circuit which combines 12kHz Subscriber Pulse Metering (SPM) detection with 18kHz tone processing for anti-fraud purposes within a telephone system. Suitable for battery or line powered systems, the MX651 is protected from crosstalk and false decoding by employing high accuracy switched capacitor filters. By using simple logic or Processor control the MX651 will: Decode 12kHz SPM pulses (in the presence of high level voice and 18kHz signaling) and provide a logic output. Transmit an NRZ amplitude modulated 18kHz security tone to line. Decode an incoming modulated 18kHz security tone (in the presence of high level voice and 12 kHz SPM tones) and provide a logic output.