3rd Party Keyless Entry DIY (Why Not?)

[Anker]

I'm too lazy to dive into it, but I believe it is much more complicated than this. The various systems communicate with one another through the CAN bus on late 986es and before that I also believe that they communicated with a protocol rather than by simply setting voltages on pins.

So the engine will refuse to start unless the immobilizer sends a message over the CAN bus (or earlier bus) that it that it is OK.