"Faraday guide: what actually blocks what"
Faraday guide: what actually blocks what
Faraday pouches and boxes are the most commonly oversold products in privacy hardware. Some genuinely work; some barely attenuate anything. This guide separates the bands, the physics, and the marketing, then matches each of our four Faraday products to the job it can actually do.
The bands you are trying to block
The signals a small radio device emits are spread across several bands, and a shield is rarely equally good at all of them:
- NFC/RFID (13.56 MHz) — tap-to-pay cards, passports, fobs. Low frequency, magnetic-field coupling, easy to shield with modest materials.
- Key fobs (typically 315/433 MHz) — the band exploited in relay attacks, where a pair of attackers extend the fob-to-car link so a parked car believes the key is present. Relay attacks on passive keyless entry systems are well documented in the academic literature — see the paper on relay attacks on passive keyless entry and start systems.
- GPS (1575.42 MHz) — receive-only on a phone. A shielded phone stops broadcasting your position to networks; GPS itself is inbound.
- Cellular (700 MHz to 2.6 GHz) — calls, SMS, LTE/5G data, IMSI. The hard band for a pouch, because any seal gap leaks.
- WiFi and Bluetooth (2.4/5 GHz) — easiest of the modern bands to kill completely with a good pouch.
Attenuation in the real world: it is all about the seal
The physics of a Faraday cage is simple; the engineering is not. Any opening — a zipper, a rolled lip, a velcro flap — acts as an RF feed and dramatically reduces attenuation. Security researcher Matt Blaze measured commercial phone-sized Faraday bags in an RF lab and found performance varies wildly between products, even when they look identical, because a few millimetres of seal gap can drop shielding from tens of decibels to almost nothing. Local Australian testing points the same way: the Hearing and Deafness Team / Tech Safety Australia Faraday Bag Testing report documents how results differ between seals on the same bag.
The practical lesson, repeated in nearly every credible test (see also It's Tactical / Offgrid Web's testing of commercial and DIY blockers): a rigid, continuously conductive enclosure outperforms a fabric pouch, and you must test your own bag with your own phone — put the device inside, call it, and confirm it rings to voicemail with no "device unreachable" delay, and check the Find My beacon is gone.
Our four Faraday products, matched to jobs
All four are stocked with products we sell in our own store, so we link them openly:
| Product | Best for | Not the right tool for |
|---|---|---|
| Faraday Keyfob Guard Box (A$9.90) | 315/433 MHz car keys, office access tokens, hotel cards. Rigid box, continuous shielding. | Blocking a phone's cellular radio — it is too small. |
| Faraday Phone Signal Pouch (A$19.90) | Taking a phone fully off the network: calls, SMS, WiFi, Bluetooth. | Carrying daily-use phones you still want to receive alerts on. |
| Faraday Laptop Sleeve 13–14" (A$49) | Travelling laptops that must not beacon on Find My or WiFi while in transit. | Working sessions — the machine has to come out to be used. |
| Faraday Tablet & Device Dry Bag 13" (A$39.90) | Tablets, chargers, spare phone, e-readers in one roll-top bag — travel and gear storage. | All-day carry of an in-use tablet. |
Practical takeaways for AU readers
- Keyfobs first, phones second. Relay-theft risk is real but niche; if you only shield one thing, a rigid box for the spare house and car keys is the cheapest high-value fix.
- A powered-off phone is not a shielded phone. iPhones can continue Find My beacons after power-down; Android "off" is a software state. Only the pouch is trustworthy.
- Test every bag on arrival with a call plus a Bluetooth scan, and re-test after wear. Seals age.
- Rigid beats fabric for the same nominal spec — the seam is the product.
This post is general information, not a guarantee of shielding performance or security. Any specific product's attenuation depends on device, band and condition — verify before relying on it for anything safety-critical.