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Ever noticed someone wrapping their car key in aluminum foil? It might look odd, but this DIY trick actually creates a Faraday cage that can block the RFID signal used by keyless entry systems, offering a simple way to deter certain types of car theft.
A smart key constantly emits a low‑frequency radio signal that allows the vehicle to unlock when you’re nearby. Criminals have learned to hijack this signal with relay devices, effectively letting them unlock and drive away the car in seconds – some reports say as little as 20 seconds. In 2025, BBC‑reported victim Abbie Brookes‑Morris shared that thieves can hover outside a home with a relay, locate the key signal, and gain access without ever entering the house.
Wrapping the key fob in foil works by forming a Faraday cage: the metal shields the signal, preventing external receivers from picking it up. When the key is completely encased in several layers of foil, the RFID transmission is essentially blocked.
Relay gadgets come in all shapes – some look like ordinary Bluetooth speakers – so the foil hack is tempting. However, it only succeeds if the foil is thick enough and forms a sealed enclosure. One or two layers will not cut it; you need multiple layers and a snug fit.
Because of these limitations, most security experts recommend using a purpose‑built signal‑blocking pouch or container for long‑term protection. Combining the key’s built‑in sleep mode (if available), a signal‑blocker, and other deterrents such as a steering‑wheel lock, can significantly reduce the risk.
Practical habits also help: store the key in the middle of the house rather than by the front door, and keep the vehicle in a garage or well‑lit area. While foil offers a low‑cost, immediate stopgap, the most reliable defense combines technology, habit, and a robust physical lock.
