Logistically, the biggest engineering challenge was miniaturization. With a Taser, two probes attach to the assailant, arcing up to 50,000 volts of electricity, enough to penetrate clothing. The XREP, on the other hand, uses just 500 volts to allow for smaller circuitry. Instead of arcing the current, it sends it directly into the body via barbed electrodes that pierce the skin. Lead XREP engineer Mark Hanchett says the key isn't so much the voltage but the waveform. The current, shaped to mimic electrical signals in the body, jams the nervous system. "The waveform is the secret sauce," he says.