[Christ]

The only legality issue would be to the holder of intellectual patent/copyright. IF given written permission to build/sell the units, be them for profit or not, there is no legality issue with it. That's IF.

There is no legality issue with copying a patent or copyright in the US FOR ONE'S OWN USE, however, copying with intent to distribute, with or without intent to profit from said copy, is illegal. (That's exactly what I remember, not exactly how it's written.) A copyright is always held by the person who originally designed/built the project, even if not properly filed with the US/foreign patent office.

IOW. If you were to copy something that was in the prototype stage, and release your copy BEFORE the other person made it to market, they could still hit you with copyright infringement, if they could prove that their intellectual property had been stolen. (Dated plans)

Even in the event that someone else built it, from what I understand, you'd still have to wire it to your ECU. If you're not comfortable with messing with your vehicle's electrical system, it might be better to take it to a mechanic or someone that does car alarms, etc. and take them the directions too, so they can put it in for you.

If anyone is interested in building them, RadioShack has project boxes that one could cut a "screen" into, and fill it with that stuff that they make blister packs for toys out of... cellophane?... to protect the unit and make it seem more "OEM" (That IS a consideration for some people.)