What Is a Faraday Bag for iPhone and How Does It Block Signals? | dB Ratings Decoded

A Faraday bag for iPhone is a conductive pouch that blocks cellular, Wi-Fi, Bluetooth, GPS, and NFC signals when fully sealed — but only if it’s built and closed right.

Leave the flap half-folded or let the phone poke through the seam and the whole thing stops working. A Faraday bag isn’t magic — it’s an enclosure, and an enclosure with a gap leaks. This guide covers what actually gets blocked, what doesn’t, and how to test a bag yourself in about a minute.

How Does a Faraday Bag Block Signals?

A Faraday bag works by wrapping the phone in conductive fabric that absorbs radio-frequency energy before it reaches the antennas, a setup engineers call a Faraday cage. The bag’s metalized layers turn incoming and outgoing signals into a small current that dissipates as heat instead of reaching the phone.

Performance is measured in decibels (dB) across specific frequencies. A higher number means more signal is stopped. A bag that claims 100 dB+ blocking tells you almost nothing on its own — you need the frequency range and the test method too. If a listing only says “military-grade” with no dB figure or lab name, treat the claim as marketing.

One manufacturer reports its bags went through independent RF-shielding testing in 2021 at AQL EMC Ltd., a UKAS-accredited lab, using a method based on MIL-STD-285 that measures finished bags rather than fabric samples. That’s a stronger standard than testing a scrap of cloth, because closures and seams are where bags fail.

What Actually Gets Blocked Inside a Sealed Bag?

A properly closed Faraday bag blocks every radio your iPhone uses: cellular calls and texts, mobile data, Wi-Fi, Bluetooth, GPS, NFC, and RFID. The phone keeps working locally — the camera, alarms, downloaded music, and notes all still function. What stops is anything that needs a network.

Apple’s own Airplane Mode documentation makes a key point here: Airplane Mode turns off cellular and Wi-Fi, but Bluetooth stays on unless you disable it separately. A Faraday bag is the only practical way to kill that remaining Bluetooth radio, plus GPS and NFC, all at once.

What the bag does not do: it doesn’t erase data, encrypt the phone, or stop someone holding an unlocked device from opening it. It also doesn’t replace a passcode, Face ID, or Lost Mode. If your goal is a locked-down phone, the bag handles signal silence — not security.

How Do You Test a Faraday Bag at Home?

The simplest test is a phone call. Place the iPhone fully inside, seal the closure exactly as the manufacturer specifies, then call it from another phone. A working enclosure should stop the normal ring — though voicemail pickup can vary by carrier, so don’t judge success by that alone.

Test Wi-Fi and Bluetooth separately if they matter. A passing cellular call doesn’t prove 5 GHz Wi-Fi or newer bands are blocked. Open the phone’s Wi-Fi list while it’s sealed — if your home network still shows up, the bag leaks at that frequency. Small bags designed for the phone and case together, like the medium 19 × 10.5 cm size listed for a large smartphone with case such as the iPhone 11 Pro Max, need real clearance so the device never touches the closure.

If you’re shopping for one, our tested iPhone faraday bag roundup compares closure designs and real dB specs side by side.

The Mistakes That Break a Faraday Bag

Most “my Faraday bag doesn’t work” complaints trace back to the closure, not the fabric. A roll-down Velcro flap has to be folded tightly with the conductive seal fully engaged; a loose fold or a phone pressed against the seam creates a path for signal.

Watch for these:

• Phone partly outside the bag or brushing the flap — the phone reconnects instantly.
• Worn seams or punctures in the conductive liner, which worsen over time.
• Testing only one frequency — a call test that passes can hide a 5 GHz Wi-Fi leak.
• Expecting GPS blocking to hide all location — the phone can retain its last known position and log data locally.
• Trusting “military-grade” with no dB figure, frequency range, or finished-bag test result.

Inspect the bag periodically and replace it once the liner shows wear. Weatherproof 400-denier nylon outer shells hold up well, but the conductive layer inside is the part doing the work — and it’s the part that expires.

Bottom line: a Faraday bag silences every radio in your iPhone when it’s fully sealed, and gives you nothing when it isn’t. Check the dB specs, test with a call and a Wi-Fi scan, and keep the closure clean. That’s the whole job.