Short version: yes, quality Faraday bags work — documented attenuation of 60–100+ dB across the relevant frequencies. Long version: the variable is product quality, and most failures trace to three predictable manufacturing or wear-related failure modes. Here is how to verify yours, what to look for in a new one, and why the question keeps coming up.
Faraday cages are well-established physics from the 1830s, deployed in industrial, military, and consumer contexts for over 150 years. Quality Faraday bags routinely achieve 60–100+ dB of attenuation — sufficient to defeat any consumer wireless threat. The reason the question keeps getting asked is that the consumer market is full of cheap and worn-out products that genuinely don't work. The fix is buying a tested product and verifying its performance every few months.
The category includes great products and bad products at every price point. A $30 phone sleeve from a quality manufacturer can outperform a $200 case from a low-quality manufacturer. The brand alone doesn't tell you whether the product works; the documented attenuation across a specified frequency range tells you whether the product works.
The rest of this article explains how to verify your own bag, what specifications matter when buying a new one, and the three failure modes that account for almost every "my Faraday bag stopped working" complaint.
The first two take 60 seconds each and catch obviously-failed bags. The third produces the documentation that procurement audits require.
Put your phone inside the bag. Close it fully. Call the phone from another phone. If the inside phone rings, the bag is leaking on the cellular and ringtone-trigger frequencies. Quick, free, 60 seconds. Limitation: works only if both phones have signal in the test environment.
Put a device inside the bag. From another device, query the location via Find My (iOS) or Find My Device (Android). Wait 5 minutes. If a current location appears, the bag is leaking on the cellular and BLE relay frequencies. Catches subtle failures the call test misses, including the BLE-only AirTag-detection vector.
For procurement-grade verification: a calibrated RF spectrum analyzer (Rohde & Schwarz, Keysight, Anritsu) sweeps the 30 MHz – 10 GHz envelope outside and inside the bag. The dB difference is the measured attenuation. Produces letterhead test reports for procurement files. Methodology aligned with IEEE-299.
If a Faraday bag fails a test, the failure is almost always one of three things. Knowing which lets you decide whether to replace, return, or upgrade.
The most common failure. Wear, washing, or manufacturing defects create tiny gaps in the conductive layer. A pinhole leak in the conductive layer is mathematically equivalent to no Faraday cage at all on the leaked frequency. Quality manufacturers test per unit; cheaper products test a sample batch and rely on consistency that doesn't always hold.
The bag's seams, zippers, and closures are where 90% of failures happen. Bad seams are not always visible. A slot-style metal zipper can leak at the gap between teeth; Velcro closures need overlap to work; folded-flap closures need to be closed correctly. Every bag has a critical closure technique — read it, follow it, test it.
Single-band shielding fabric used for full-spectrum claims. A fabric tested only for 13.56 MHz RFID will leak at 2.4 GHz Bluetooth or 5G cellular. "Faraday-rated" without a specified frequency range is a marketing claim, not a specification. Look for products that state the tested envelope (e.g., 30 MHz – 10 GHz) and the dB attenuation across that envelope.
"Faraday-rated" and "blocks all signals" are marketing claims. The specification you want is a dB number across a stated frequency range — for example, "76–85 dB across 30 MHz – 10 GHz". 60 dB defeats most consumer threats; 70 dB defeats nearly all professional threats; 80 dB+ provides industrial-grade isolation. Above 85 dB, additional attenuation provides diminishing real-world benefit.
The relevant envelope for consumer threats is 30 MHz – 10 GHz. That covers all mobile cellular bands (including 5G mmWave within reasonable bounds), all WiFi standards including WiFi 7, all Bluetooth and BLE, all GPS bands, NFC, RFID, and key-fob LF/UHF. Products tested only at specific narrow frequencies (e.g., RFID 13.56 MHz only) are appropriate for narrow use cases, not for general signal isolation.
Better manufacturers test every unit before shipping, so the documented attenuation is a per-unit guarantee. Cheaper manufacturers test a sample from each batch and rely on consistency. The first approach catches manufacturing defects that the second does not. Ask the manufacturer how testing is done.
Three cues that predict longevity: overlapping conductive seams (no pinhole gaps), continuous-conductor closures (not slot-style zippers), and structured form factor (not soft-sleeve, which creases the conductive layer at fold points). A structured executive briefcase has fewer wear-related failure points than a soft pouch carried in a backpack.
Works in theory if wrapped completely and tightly. In practice, household aluminum foil tears, creases, and pinholes constantly during normal handling. Re-wrapping the device every time is not a sustainable defense.
Has a metal-mesh viewing screen that leaks at relay-attack frequencies. Will attenuate some signal but not enough to defeat quality amplifiers. Don't.
Plastic exterior with metal panels — not a continuous-conductor enclosure. The same partial attenuation as the microwave; not a replacement for a tested Faraday product.
Sometimes works, sometimes doesn't. A continuous welded-steel safe with no gaps will perform like a Faraday cage. A typical home safe with hinge gaps, lock-pin holes, or a non-welded seam will leak. The advantage of a documented Faraday bag is that the attenuation is specified; with a generic safe, you don't know until you test.
Three independently shielded chambers, 76–85 dB attenuation across 30 MHz – 10 GHz, structured executive briefcase form factor, made in the United States. The documented attenuation is the per-unit guarantee, not a marketing aspiration. $129 with free U.S. shipping and 30-day money-back guarantee.
Acquire — $129 Read the Faraday 101 Hub