The pentagon’s ray gun can stall cars – slashdot gas dryer vs electric dryer cost savings

That shielding won’t save you, and is actually the point! The shielding absorbs the energy, causing a large transient voltage spike in your car’s electrical system. That causes the ECU to crash, because it isn’t designed for those conditions.

One of the key things to understand here is that the car only has two electrical connections, battery + and battery -. Battery – is often called "ground," it will tend to be at local ground because it is referenced to the vehicle chassis which will likely be at ground potential when you start the car. But it doesn’t have a third wire with an actual Earth connection, and the wheels are usually electrical insulators. What that boils down to is that shielding works by converting the RF interference into a short voltage spike, some of which is converted to heat in the ECU and any other electronics with voltage regulation. All the devices in the car are already expected to survive "double battery condition," which is when the tow truck driver gives you a jump start using 24V, which is really 28V+ because their engine is running and their battery is charging voltage. So there is a huge amount of voltage margin and the shielding works well without even having system-wide voltage regulation. But in the extreme case, as with this device, you eventually overload the ECU’s voltage regulation, and since the circuit is designed to be robust, it simply crashes and reboots as soon as the spike dissipates. Repeated use could easily damage a vehicle, though.

It’s not just efficiency, it’s basically ease of operation. One of the big things about modern cars is they are "twist and go". You twist the key (or push the button nowadays) and the car goes. Doesn’t matter if the engine is hot (vapor lock is not an issue), very cold, or any other thing, including poor fuel. You want it to go, it goes, and unless something is very wrong, it will go. (You can even shoot out cylinders and while it stalls the engine, you can have a V8 engine with 6 dead cylinders still barely run. It’s not happy, but the computer is able to compensate and get you home, albiet slowly).

Anyhow, did you wonder why it took 300kW to do it? It’s because an ECU is very well shielded to begin with – the metal body of the car already is a great faraday cage. But the ECU is also encased in a metal body because it’s a very challenging environment with a lot of stray RF caused by all the high voltages around.

In fact, if you’re willing to settle for post-millennium vehicles, disrupting the keyfob-car communications will generally be far easier – the windows in the passenger compartment don’t generally block RF, and the signal levels are weak since keyfobs are powered by itty coin cell batteries with poor peak power performance, so they don’t have much transmit power. (I had to replace the battery in my keyfob – it still measured 3V, while batteries that are generally dead used in PCs measure pretty damn close to 0.5V. Heck, even my watch which died suddenly had a battery that measured around 0.5V. No doubt the battery was low, so it couldn’t supply the necessary power for the transmitter)