The slot interposer probe consists of a board with a male edge connector and a female edge connector connected to its opposed edges and circuitry electrically connecting the male edge connector to the female edge connector. The female edge connector may be a straddle-mount connector. The board may have an inner layer sandwiched between two outer layers. There may be a probe having a high-speed buffer connected to a plurality of capacitors, isolation resistors, and vias that intercepts signals carried by transmission lines on the inner layer. The vias may have a length equal to the inner layer's width. The high-speed buffer receives intercepted signals from the vias, copies and amplifies the signals, and drives them through coaxial cables to an acquisition module. The invention also includes a method of intercepting signals between a first electrical device and a second electrical device.