Do Faraday Boxes for Car Keys Work? A Complete Guide

If you drive a modern car, your keyless fob is constantly broadcasting a signal. Thieves can capture that signal with a relay device and unlock your car in seconds, without ever touching your keys, according to CarGurus UK (automotive research site). A Faraday box – a simple, conductive enclosure – can block that signal entirely.

Signal blocked: Key fob radio frequencies (CarGurus UK) ·
Police stance: Recommend Faraday bags for key fob protection (Police1 (law enforcement publication)) ·
DIY material: Galvanised steel with tight seal (CarGurus UK)

Six key facts about Faraday boxes, one takeaway: a well-made enclosure is a reliable shield, but only if used correctly.

This guide breaks down how they work, which ones are worth your money, and what you can use in a pinch.

Do car key Faraday boxes work?

How do Faraday boxes block key fob signals?

• Faraday boxes are enclosures made of conductive materials (copper, aluminium) that create an electromagnetic shield (CarGurus UK).
• When a key fob is placed inside, the conductive shell absorbs and redirects the radio-frequency signal, preventing it from reaching the car.
• The box must be fully closed and the key must not touch the metal – contact can turn the box into an antenna (CarGurus UK).

Do cheap Faraday boxes work as well as expensive ones?

• According to RAC Forum discussion, basic pouches can work if the conductive lining is intact and the seal is tight.
• However, low-cost models often use thin fabric that wears out, and repeated use can weaken the shielding (RAC Forum).
• Expensive boxes (e.g., metal containers) tend to have thicker material and better seals, making them more reliable over time.

The pattern: price reflects build quality. A £10 pouch might work for a week, but a £40 metal box is likely to last years.

What are Faraday bags and how do they prevent car theft?

What is the difference between a Faraday bag and a Faraday box?

• A Faraday bag is a flexible pouch lined with conductive mesh, while a Faraday box is a rigid container (CarGurus UK).
• Both work on the same principle, but boxes generally offer more consistent shielding because the metal enclosure has fewer gaps.
• Bags are more portable, but their seal can degrade over time (RAC Forum).

How does keyless car theft work (relay attack)?

• Thieves use two relay devices: one near the key fob (inside the house) and one near the car. The first device captures the fob’s signal and transmits it to the second, which tricks the car into unlocking and starting.
• According to Police1 (law enforcement publication), Faraday bags block this relay by preventing the fob from transmitting any signal.
• The attack range can be up to 100 meters, though most thefts occur within a few dozen metres.

What can I use instead of a Faraday box?

Does a biscuit tin work as a Faraday box?

• A metal biscuit tin can block the signal if it is entirely metal and the lid fits snugly, says CarGurus UK.
• However, alloy containers (like galvanised steel) work better than plain tin (CarGurus UK).
• You also need conductive tape to seal any gaps – a biscuit tin with a rubber or plastic rim will leak signal (RAC Forum).

Is a fridge a Faraday cage?

• According to RAC Forum discussion, a refrigerator is not a reliable Faraday cage because of the rubber door seals and the non-conductive interior parts.
• The metal shell can reduce some signal strength, but gaps and plastic components allow enough leakage to be exploited.
• It is not recommended as a secure storage solution for key fobs.

How to make a DIY Faraday cage with aluminum foil

• Multiple layers of aluminum foil wrapped tightly around the key fob can create a temporary Faraday cage, according to a YouTube test (DIY signal blocking).
• The key is to ensure there are no holes or gaps – even a small gap can let the signal through (YouTube test).
• This is a temporary fix; a dedicated Faraday box offers far more consistent protection.

What is a police approved Faraday box for car keys?

How to identify a police approved Faraday box?

• UK police forces (e.g., Warwickshire Police) recommend the use of Faraday bags or boxes as a preventive measure (Police1).
• There is no official “police approved” certification. Instead, products from trusted brands like Halfords and Defender are commonly recommended by officers.
• Look for products that explicitly block ultra-high frequencies (UHF, GPS, Wi-Fi) up to 10 GHz, as these cover the bands used by keyless entry systems.

Are there official certification standards?

• No universal standard exists. Each police force may recommend different products based on local tests.
• The best guidance is to choose a Faraday box that is fully metal, has a tight-fitting lid, and is tested by independent reviewers.

The implication: “police approved” is a marketing term, not a stamp of quality. A metal box from a reputable brand is your safest bet.

Which is better RFID blocker or Faraday?

What is the difference between RFID and Faraday blocking?

• RFID blockers are designed to block specific radio frequencies used by credit cards and passports (125 kHz, 13.56 MHz).
• Faraday cages block a much broader spectrum – from low frequencies up to 10 GHz – which includes key fob signals (315/433/868 MHz) as well as GPS and Wi-Fi.
• According to CarGurus UK, Faraday bags are often called RFID blockers, but the Faraday type offers wider protection.

Do I need an RFID blocker for car keys?

• No – a narrow RFID blocker may not cover the frequencies used by your key fob.
• For car key theft prevention, a Faraday box or bag that covers the 0–10 GHz range is the right choice (CarGurus UK).
• If you also want to block contactless payment cards, look for a product that states “RFID blocking” alongside “Faraday” protection.

How to choose the right Faraday box for your car keys

The table below distills the key factors that separate an effective Faraday box from a waste of money.

The pattern across five product categories: the best Faraday box balances material quality, seal integrity, and size. Cheap pouches may fail after a few uses; a solid metal box is a permanent solution.

Pros and cons of different Faraday options

How to test your Faraday box at home

1. Place your key fob inside the Faraday box and close it completely.
2. Walk to your car and try to unlock it normally. If the car does not unlock, the signal is blocked.
3. If the car opens, check the box for gaps or make sure the key is not touching the metal (CarGurus UK).
4. Repeat the test with the key in different positions inside the box.
5. For extra reassurance, use a portable AM/FM radio – if the signal disappears when you close the box, the shielding is working.

For UK drivers, the choice is straightforward: buy a solid metal Faraday box from a trusted brand, or seal a biscuit tin with conductive tape. The cheapest solution is only effective if the seal holds. The safer route is a certified metal box that will not wear out.

Related reading: What Is a Biometric Passport? Symbol, Chip & How to Check · DVLA Driving Licence Changes: Address, Renewal & Over 70 Rules

If your model is not affected by built-in immobiliser weaknesses, a standalone Faraday box remains a solid backup, and for shoppers across the Irish Sea we have also rounded up top options for Ireland in 2024.

Frequently asked questions