Immobilizer system method of operation? (or alternative non-janky, theft deterrent)
 

I know Reverent has figured this out, and i'm not asking for proprietary information, but if anyone can give me some idea of how the immobilizer communicates with the stock ECU it would be helpful. I know the stock immobilizer system is not the highest grade of security, but having it functional with my MSPnP pro would give me some piece of mind.

Is this something that might be doable with the standard CanBus system, or is this something that would need a special chip?

Alternatively, any ideas on convenient theft control that won't make my car unreliable? I'd really like to be able to drive my car to work and not worry (quite so much) about it being stolen.

A toggle switch on one or more of the relays, fuel pump, main, etc. Do it on the relay activation or the activation ground and not on a power supply leg.
One thing that works better than anything else for a casual thief is a removable steering wheel. You have to take it with you but it's really effective.
Thieves avoid cars with no steering wheels, and this is EASY to see. Probably keep your windows or top from being destroyed as well.

One last suggestion is some form of locating device. Apple air tag, other tracking device. There are many inexpensive solutions for this now.
A decade ago, we had a Lojack installed on a new car. It has never failed. It still texts us today if the batteries run out in the fobs. "Your car has been moved without your permission"...
It was expensive back then, but it has worked flawlessly.
Many major cities have police cars that can work with Lojack. The cop car itself can find your vehicle.
Lojack style systems, installed in a hard-to-find area, are extremely effective at theft recovery. My car has no stickers or any evidence that the system is installed.

Factory immobilizers are commonly used across many models from the same manufacture and thieves learn the work arounds shortly after the devices hit the market.
If a professional thief wants your car you are screwed. Make sure to keep comprehensive insurance on your vehicle and having a pre-determined value can help big time.

Thanks. Now that I think of it, the new FP relay will be in the trunk area. I can easily add a toggle back there that can interrupt the fuel pump wiring.

The 2001-2005 MSPNPPro has a jumper to allow or ignore use of the OE immobilizer system on 2001+ USDM miatas. If you are talking about other custom methods for immobilizing the car, yes, plenty of systems you could interrupt with a manual switch of some sort.

You have a 01 NB. The little oval finisher plugs that cover the forward console mounting bolts make a wonderful place to place a rocker switch. Find the right rocker switch (black and oval) and it disappears when mounted in the car.
I'd use the passenger side one for a place to put your FP relay kill switch.
Best feature of this position is you only modify the little cover. No holes in anything important.

Another good location is inside the console box, but this is much easier to find by a thief.

Thanks boileralum. I didn't know that and it helps me

Best location for a (fuel pump) kill switch is under the shift boot.
Had it set up like this on a '99 civic I owned.

You can flip it through the boot and it doesn't show to the outside world.

I would interrupt the signal from the crank sensor to the ECU. The fuel pump is way too predictable.