An interlock monitoring system includes a magnetic proximity sensor within a poppet valve type coupler to detect whether the poppet valve is opened or closed. An open poppet valve indicates a proper connection. The sensor consists of dedicated electronics that prevent cheating, or bypassing, by either shorting out or opening the contacts to the sensor. In addition, a ferrous metal proximity switch is used to provide a redundant confirmation of proper connection of the coupler. The ferrous magnetic proximity switch will indicate whether or not the coupler is actually in contact with an appropriate connection. Each of the magnetic proximity sensor and the ferrous magnetic proximity switch must indicate a respective proper condition in order to determine a valid interlock condition.