Faraday Cage Guide: Protect Your Electronics from EMP
A Faraday cage is your primary defence against electromagnetic pulse (EMP) damage to critical electronics. Named after physicist Michael Faraday, a Faraday cage is any conductive enclosure that prevents external electromagnetic fields from reaching the contents inside. For EMP preparedness, this means storing your emergency radios, backup phones, medical device controllers, and other critical electronics in a shielded enclosure so they survive a nuclear EMP or solar CME event and are available when you need them most.
This guide covers how Faraday protection works, what DIY options actually perform adequately, which commercial products are worth buying, and exactly what to store in your Faraday cage for a complete EMP preparedness strategy.
How Faraday Cages Actually Work
A Faraday cage works by redistributing the electromagnetic charge around the exterior of the cage, creating a cancellation field inside. Key principles for EMP protection:
- Conductive material: The cage must be made of electrically conductive material: metal mesh, foil, or solid metal. The gaps must be smaller than the wavelength of the electromagnetic pulse being blocked.
- No gaps: For nuclear E1 EMP, you’re blocking very high-frequency, fast-rise-time pulses. Any gap larger than a few centimetres can allow penetration. Lid seams and door edges are the most critical areas.
- Insulation inside: The contents must not contact the metal of the cage. If a device touches the cage wall, it can receive conducted (not radiated) voltage spikes. Always line interior with cardboard, foam, or fabric.
- Grounding (optional): A grounded Faraday cage is more effective for E3 (the slow component from solar CMEs). For E1, grounding is less critical than having no gaps.
DIY Faraday Cage Options (Tested & Rated)
Option 1: Metal Garbage Can (Recommended DIY)
A galvanized steel trash can with a tight-fitting lid is the most commonly recommended DIY Faraday solution: and it actually works. The all-metal construction with a lapped lid creates a reasonable seal against E1 EMP frequencies.
- What you need: 20-gallon or larger galvanized steel trash can; copper tape; cardboard lining
- Build instructions: Line interior with cardboard (don’t let devices touch metal). Seal the lid-to-can junction with copper tape on the exterior. Lay contents on cardboard. Close lid.
- Effectiveness: Good (3-4 layers of attenuation); not lab-tested but widely validated by EMP researchers
- Cost: $40–$70 for the can + $10 copper tape
Option 2: Military Surplus Ammo Cans
M2A1 or M19A1 metal ammo cans with gasket seals are excellent Faraday containers for smaller electronics. The all-metal construction and rubber gasket create a nearly seamless enclosure.
- Great for: Radios, phones, dosimeters, USB drives, charge controllers
- Cost: $20–$40 per can at military surplus stores or Amazon
- Limitation: Size: limited to smaller electronics
Option 3: Aluminium Foil Wrapping
Wrapping in multiple layers of aluminium foil provides moderate EMP protection and is the simplest DIY option.
- Method: Wrap device in cardboard first (insulation). Then wrap in 2–3 layers of heavy-duty aluminium foil, ensuring full coverage with no gaps or tears. Smooth foil tightly.
- Effectiveness: Moderate: good for lower-intensity EMP but not guaranteed against nuclear E1. Better for solar CME scenarios.
- Cost: Minimal: heavy-duty foil at $10/roll
Commercial Faraday Options Reviewed
Faraday Bags (Flexible)
Commercial EMP bags use multiple layers of woven conductive fabric (often copper/nickel blend) with sealed closures. Quality varies significantly between brands:
| Brand | Shielding Level | Best For | Price Range |
|---|---|---|---|
| Mission Darkness | Military MIL-STD-461 verified | Phones, tablets, radios | $30–$80 |
| DefenderShield | High (independently tested) | Laptops, devices | $40–$90 |
| Faraday Defense | High (self-reported) | General electronics | $20–$60 |
| Generic Amazon bags | Variable (unverified) | Not recommended for critical gear | $5–$20 |
Rigid Faraday Enclosures
Rigid commercial Faraday boxes provide higher attenuation than bags: important for nuclear E1 scenarios:
- Abigail 40-gallon Faraday cage: Purpose-built EMP-protection chest; laboratory-tested; ~$400
- Ready Made Resources Faraday cage: Customisable prepper-focused enclosures; ~$200–$500
What to Store in Your Faraday Cage
Priority Tier 1 (Essential)
- Hand-crank emergency radio (your post-EMP information source)
- Spare ham radio transceiver (Baofeng UV-5R or equivalent)
- Spare mobile phone (loaded with offline maps, reference documents, survival guides)
- USB drives (digital copies of all documents, offline maps, medical records)
- Radiation dosimeter/Geiger counter
- Solar charge controller (spare: your existing one will likely be damaged)
- Medical device controllers (CPAP controller, insulin pump manager, etc.)
Priority Tier 2 (Important)
- FRS/GMRS two-way radios (family communication)
- Spare laptop (with offline survival library)
- Battery-powered LED lanterns
- Spare car ignition module/ECU (for post-2000 vehicles)
- Rechargeable batteries + charger
How to Test Your Faraday Cage
A simple field test: put your phone inside your Faraday cage and close it completely. Then call the phone’s number from another phone. If you get voicemail immediately (no ringing inside), the cage is blocking cell frequencies. If it rings, your seal has gaps.
Top Product Picks
Mission Darkness MOLLE Faraday Bag Kit
Mission Darkness makes the most consistently reviewed commercial Faraday bags: with independent MIL-STD-461 verification. The MOLLE kit includes multiple bag sizes for different devices: phone pouch, tablet bag, and a larger general-purpose bag. A complete set covers all your Tier 1 and most Tier 2 electronics. The MOLLE attachment system also allows mounting to a bug-out bag for portable EMP protection.
- MIL-STD-461 independently verified shielding
- Multi-size kit: covers phones, tablets, and radios
- MOLLE-compatible for backpack attachment
Behrens 20-Gallon Galvanized Steel Trash Can with Lid
The classic DIY Faraday cage foundation. Behrens galvanized steel trash cans have all-metal construction including the lid and handle: no plastic components to create conductive gaps. The tight-fitting lipped lid creates a reasonable EMP seal that can be improved with copper tape. Large enough to hold a power station, radios, laptop, and spare electronics. At $50, it’s the most cost-effective large Faraday container available.
- All-galvanized steel: no plastic components
- 20-gallon capacity: holds full electronics kit
- Tight-lipped lid seals well with copper tape addition
SDS Importers Copper Foil Tape with Conductive Adhesive (2-inch × 33ft)
The essential finishing material for a DIY Faraday cage. Copper tape with conductive adhesive creates an electrically continuous seal at the lid-to-can junction of your galvanized trash can Faraday cage. Apply around the entire perimeter of the lid overlap to close the most common gap in DIY Faraday enclosures. Also useful for sealing gaps in ammo can gaskets. One roll is enough for multiple containers.
- Conductive adhesive: creates electrically continuous seal
- 2-inch width: ideal for lid-gap sealing
- 33ft per roll: enough for multiple Faraday projects
Faraday Cage FAQ
Does a Faraday cage need to be grounded?
For E1 nuclear EMP protection: no. Grounding is more important for E3 (the slow solar CME component) which induces persistent currents. For the fast E1 pulse, the key is having a complete, gap-free enclosure. For a combined E1+E3 scenario (nuclear EMP), a grounded, gap-free metal enclosure provides the best protection, but even an ungrounded sealed metal container provides significant E1 attenuation.
Will a Faraday cage protect against solar CME?
Partially. A major solar CME (like the 1859 Carrington Event) primarily produces E3-type slow magnetic flux changes that induce current in long conductors like power grid transmission lines. Your home electronics and devices have shorter conductors and are less vulnerable to E3 than the grid infrastructure itself. Your grounded metal Faraday cage with good electrical continuity helps, but the main threat from a CME to your devices is via induced surges through any connected wires: unplug all devices from outlets and ethernet during a CME event if you have advance warning.
What’s the difference between a Faraday bag and a Faraday cage?
A Faraday bag (flexible fabric) is portable and convenient, with good RF attenuation: ideal for phones, radios, and smaller electronics. A Faraday cage (rigid metal enclosure) generally provides higher attenuation, especially for lower frequencies associated with nuclear EMP E1. For critical electronics you depend on post-EMP, a rigid metal enclosure like a galvanized trash can or ammo can is preferred. Use Faraday bags for portability and everyday carry, cages for primary storage of your most important gear.