I guess this is a rather crude device that simply uses the factory detonation sensors, connected to pins 23 and 24 (Detonation sensors for Cylinders 1-3 and Detonation sensor 1 for Cylinders 4-6) ?
These sensors tell the factory Nissan ECCS ECU that knocking is occuring to allow it to retard the ignition a little to try to cure it. More advanced (i.e. modern ecu's) now also have sensors on the shock absorbers which detect if the detonation was due to road conditions or not.
The ECCS ecu is well over a decade old (its positively arcane by todays standards and runs at only 3Mhz, by comparison a typical pc now runs at 2,000Mhz !!)...
T