Faraday bags are used to protect electronic devices from wireless access, tracking, and unauthorised communication. They are commonly used for smartphones, laptops, tablets, and vehicle key fobs. However, not all Faraday bags provide the same level of protection, and many fail to block all relevant signals despite appearing effective at first glance.
Testing a Faraday bag properly is the only reliable way to confirm whether it delivers real-world signal isolation. This guide explains why proper testing matters, how to test Faraday bags correctly, and how to interpret the results for different use cases.
Why Proper Faraday Bag Testing Matters
Faraday bags are often relied upon in situations where wireless exposure presents a real risk – vehicle theft, data interception, tracking, or unauthorised access to devices. When a Faraday bag is not tested thoroughly, it can create a false sense of security, leaving devices exposed without the user realising it.
A common issue is partial shielding. Many low-quality or poorly designed Faraday bags block basic cellular signals but still allow higher-frequency signals such as Wi-Fi, Bluetooth, GPS, or RFID to leak through. These higher-frequency signals are frequently exploited in real-world attacks.
Proper testing ensures that a Faraday bag provides effective signal isolation across the frequencies that matter for its intended use, not just under ideal or limited conditions.
How Faraday Bags Work
Faraday bags work by enclosing a device inside conductive shielding material that disrupts electromagnetic fields. When properly constructed and fully sealed, the shielding prevents wireless signals from entering or leaving the enclosure.
The effectiveness of a Faraday bag depends on several factors:
- The quality of the shielding material
- The frequencies it is designed to block
- The integrity of seams, folds, and closures
- How the bag is used and sealed
Different devices operate across different frequency ranges. As a result, not all Faraday bags are interchangeable across use cases.
- Car key fobs typically operate on narrow frequency bands used for vehicle access systems.
- Smartphones, tablets, and laptops emit and receive a broad range of signals, including cellular, Wi-Fi, Bluetooth, GPS, and sometimes NFC.
This difference is important when testing and evaluating performance.
For a more detailed explanation of the underlying principles, see our guide on How Faraday Bags Work.
How to Test Your Faraday Bag
Testing your Faraday bag properly ensures it delivers full signal isolation across all relevant frequencies – not just mobile networks. The following steps provide a reliable assessment.
Cellular Test (Basic Check)
Place your smartphone inside the Faraday bag and seal it completely.
Ask someone to call your number.
If the call fails to connect, the bag is attenuating cellular signals.
Important: This is only a basic check. Many low-shielding Faraday bags pass this test while still leaking other signals.
Wi-Fi and Bluetooth Test (Critical Check)
Turn on both Wi-Fi and Bluetooth on your device.
Place the device inside the sealed Faraday bag.
Using another device such as a laptop or tablet:
- Search for the phone’s Wi-Fi hotspot or network presence
- Attempt to detect the phone via Bluetooth pairing
If the device still appears or can be detected, the bag is not providing full shielding against high-frequency signals.
This step is critical, as Wi-Fi and Bluetooth leakage is one of the most common failure points in poorly constructed Faraday bags.
Testing Faraday Bags for Car Key Fobs
Why Key Fobs Require Separate Testing
Car key fobs operate using specific radio frequencies designed for short-range communication with vehicles. These signals are frequently targeted in relay attacks, where criminals capture and relay the key fob’s signal to unlock or start a vehicle without physical access.
Unlike smartphones, key fobs do not transmit across a wide range of frequencies. For this reason, effective key fob protection does not necessarily require multiple shielding layers, provided the shielding material is high quality and matched to the relevant frequencies.
A well-designed Faraday bag using a single layer of high-performance shielding material can be sufficient to block key fob signals when correctly constructed and tested.
How to Test a Faraday Key Fob Bag
Place the key fob inside the Faraday bag and seal it fully.
Stand close to the vehicle and attempt to unlock the doors or start the engine.
If the vehicle does not respond, the bag is blocking the key fob signal.
For reliable results:
- Test at different distances from the vehicle
- Repeat the test several times
- Ensure the bag is fully sealed during each attempt
A properly functioning key fob Faraday bag should consistently prevent vehicle access while the key remains inside.
When a Single Shielding Layer Is Enough and When It Isn’t
The number of shielding layers required depends entirely on the application.
- Key fob protection: Often achievable with a single high-quality shielding layer designed for the correct frequencies.
- Smartphones and connected devices: Typically require broader frequency coverage, which is often achieved through multiple shielding layers working together.
A Faraday bag should be evaluated based on performance, not assumptions about thickness or layer count. This is why testing remains essential regardless of design claims.
What a Properly Built Faraday Bag Should Do
A properly built Faraday bag should provide predictable and repeatable results when tested correctly. Depending on its intended use, it should:
- Prevent wireless communication when fully sealed
- Block the frequencies relevant to the protected device
- Maintain shielding integrity at seams and closures
- Perform consistently across multiple tests
- Deliver protection without relying on device settings
If any signal passes through during testing, the bag is not delivering complete protection for that use case.
Environmental Factors That Can Affect Testing Results
Testing results can vary depending on environmental conditions. Factors that can influence results include:
- Urban environments with dense wireless traffic
- Proximity to signal sources such as routers or vehicles
- Device orientation inside the bag
- Battery state or transmission power of the device
For the most reliable assessment, tests should be repeated in different locations and conditions.
Common Faraday Bag Testing Mistakes
Many users unknowingly perform incomplete or misleading tests. Common mistakes include:
- Testing only mobile calls and ignoring Wi-Fi or Bluetooth
- Not fully sealing the bag during testing
- Assuming thicker fabric automatically equals better shielding
- Testing in only one location
- Relying on marketing claims instead of real-world tests
Avoiding these mistakes helps ensure test results accurately reflect real-world performance.
Why Some Faraday Bags Fail in Real-World Use
Faraday bags usually fail due to design or construction limitations rather than the concept itself. Common causes include:
- Inadequate shielding material
- Poor seam bonding or stitching
- Ineffective closure design
- Inconsistent manufacturing quality
A bag may block one type of signal while allowing others to pass, which is why comprehensive testing is necessary.
How Often Should You Test a Faraday Bag?
It is good practice to test a Faraday bag:
- When first purchased
- After prolonged or heavy use
- If the bag becomes damaged or worn
- When protecting a new type of device
Regular testing helps ensure continued performance over time.
Final Thoughts on Faraday Bag Testing
Testing a Faraday bag properly is the only way to confirm that it provides real protection against wireless access, tracking, and unauthorised communication. A bag that blocks mobile calls but leaks Wi-Fi, Bluetooth, or RFID signals may still leave devices vulnerable.
Understanding how to test Faraday bags and how different devices require different shielding approaches allows users to make informed decisions about their digital security.
If you would like to see examples of Faraday bags designed for specific devices and use cases, you can explore our range of Faraday protection solutions.