This is the corner of home resilience with the worst signal-to-noise ratio. There is real physics here and real historical precedent, and there is also an entire industry selling fear. The useful position is neither dismissal nor panic: understand the mechanism, note that the preparations that help are mostly the same ones that help in an ice storm, and refuse to spend money on the parts that are theater.

What actually happens, mechanically

A high-altitude nuclear detonation produces a pulse usually described in three components. The fast one, E1, is a very brief, very high-voltage field that couples into short conductors — circuit board traces, cables, antenna leads — and can damage semiconductors directly. The slow one, E3, behaves much like a severe geomagnetic storm: it induces currents in very long conductors such as transmission lines, and its main threat is to large power transformers, which are custom-built and can take a long time to replace.

A severe solar storm produces the E3-like effect without E1. There is a documented precedent: the March 1989 geomagnetic storm collapsed the Hydro-Québec grid in about ninety seconds and left several million people without power for roughly nine hours. That is the shape of the realistic risk — a wide-area, long-duration outage caused by damage to grid infrastructure, not a movie where every device on earth stops at once.

What is oversold

• “Every car will stop.” Testing has generally found most vehicles unaffected or briefly disrupted at field strengths that damage unshielded electronics; some stall and restart. Treat blanket claims in either direction with suspicion.
• Devices that are unplugged and switched off are far less exposed than devices connected to long wiring runs, because the wiring is the antenna. This is why a spare radio in a metal box is a reasonable, cheap hedge.
• “EMP-proof” generators and solar kits. A generator’s vulnerability is in its electronic controls and the wiring it is attached to. A sticker does not change that, and no consumer product has been meaningfully certified against E1 for household use.
• Timeline claims measured in years. They come from worst-case modeling, not from observation. Nobody has data for an event that has not happened.

Faraday cages: what they do and do not do

A Faraday enclosure is a continuous conductive shell around a device. It works by making the outer surface carry the induced current instead of the contents. Three practical rules follow from the physics: the shell must be continuous with no significant gaps, the contents must not touch the conductive layer, and anything with a wire leaving the enclosure is not protected. A cardboard-lined metal trash can with a tight lid, a sealed metal ammo can, or a commercial shielded bag such as those from Mission Darkness all satisfy the basic requirement. Prices run roughly $25-$120 for bags at the time of writing, and near zero for a can you already own.

What belongs inside is a short list: a spare AM/FM/shortwave radio, a spare inverter or charge controller, a backup phone, a solar panel controller, and copies of important documents on a drive. Storing your only radio in a cage is worse than useless, because you will not have it during the ordinary outage that is a thousand times more likely.

Proportionate spending

Measure	Rough cost	Useful in an ordinary outage too?
Two weeks of water, food, heat and sanitation	$1,500-$4,000	Yes — the same preparation, every time
Whole-house surge protection	$300-$700 installed	Yes — lightning and utility switching
Shielded bag or metal can with spare radio and controller	$0-$150	Partly — the spares are useful anyway
Non-electronic backups: hand pump, wood heat, paper maps	varies	Yes
“EMP-hardened” branded gear	premium priced	No

The pattern is hard to miss. Almost everything that helps in a long grid-down event is something you would want anyway, which is a good reason to build it in the order set out in Start Here rather than around this scenario. The specifics live in Power & Backup, Water, Heat & Cold and Food Storage, and the duration question is handled in By Scenario.

Latest in this section