Going Dark: Why You Need a Faraday Bag
I didn't originally plan to dive this deep into Faraday bags, but the more I researched, the more I appreciated the significant security they offer.
I initially thought I'd just discuss how smartphones use various radios for tracking and how a Faraday bag silences those signals. While that's still true, and we'll explore it further, the usefulness of Faraday bags extends far beyond just quieting your phone.
What is a Faraday Bag?
A Faraday bag is a shielded pouch designed to block electromagnetic fields, specifically radio frequency (RF) signals. It's named after scientist Michael Faraday, who invented the larger Faraday cage based on the same principle. The bag creates a protective barrier, preventing external signals from reaching devices inside and effectively isolating them from wireless communication.
How It Works
Faraday bags are typically made from conductive materials, such as metalized fabric or mesh, which absorb or reflect electromagnetic waves. When you place a device like a smartphone or laptop inside, it can no longer receive or send signals. This means Wi-Fi, Bluetooth, GPS, and cellular data are all blocked, preventing the device from connecting to networks or being accessed remotely.
How They Track Us
Modern smartphones are packed with radios that enable a vast array of functions. However, each of these radios, while designed for communication, also creates a potential avenue for tracking. It's not just one system at play; it's a sophisticated, often overlapping, network of signals that can reveal your location and movements.
Here's how a person can be tracked using the various radios on a modern smartphone:
Cellular Radio (GSM, 3G, 4G LTE, 5G):
- Cell Tower Triangulation/Multilateration: Your phone constantly communicates with nearby cell towers to maintain a network connection, even when you're not on a call or using data. By measuring signal strength or the time it takes for your phone's signal to reach multiple towers, network operators can pinpoint your approximate location. In dense urban areas, this can be accurate down to tens of meters; in rural areas, it can be miles.
- IMSI Catchers (Stingrays): These devices, often used by law enforcement or intelligence agencies, mimic legitimate cell towers. Your phone will connect to the IMSI catcher, which can then force it to reveal its unique International Mobile Subscriber Identity (IMSI) and other identifiers. Some advanced IMSi catchers can even intercept calls and texts and track your precise location.
- Network-Based Location Services: Your mobile carrier knows which cell tower your phone is connected to at any given moment. This data, even when aggregated and anonymized, can infer movement patterns. While carriers claim to protect this data, there have been instances where such location data has been sold to third parties.
Wi-Fi Radio:
- Wi-Fi Scanning and Probe Requests: Your phone's Wi-Fi radio constantly scans for available Wi-Fi networks, even if you're not connected. During this scanning, it sends out "probe requests" that can contain your device's MAC address (a unique hardware identifier, though modern phones often randomize this) and a list of previously connected Wi-Fi networks.
- Wi-Fi Positioning Systems (WPS): Companies like Google and Apple maintain extensive databases of Wi-Fi access point locations. When your phone detects these known Wi-Fi networks, it can send their unique MAC addresses and signal strengths to a WPS server, which then uses this information to determine your location, often with greater accuracy than cellular triangulation, especially indoors.
- Retail and Public Wi-Fi Tracking: Many businesses and public spaces use Wi-Fi networks to track foot traffic, customer dwell times, and repeat visits by monitoring signals from devices that are scanning for Wi-Fi, even if they don't connect.
Bluetooth Radio (including Bluetooth Low Energy - BLE):
- Bluetooth Beacons: Small, low-power Bluetooth transmitters are deployed in various locations. Your phone, with Bluetooth enabled, can pick up these signals, allowing apps or tracking systems to know your precise location within that indoor environment, trigger notifications, or offer localized services.
- "Find My" Networks (e.g., Apple's Find My Network, Google's Find My Device Network): These extensive networks use the Bluetooth signals of millions of devices to help locate lost items. If your device is lost, any nearby device in the network can detect its Bluetooth signal and securely relay its location back to you. While incredibly useful, it illustrates how Bluetooth can facilitate widespread, anonymous location reporting.
- Device-to-Device Proximity: Apps can use Bluetooth to determine your proximity to other Bluetooth-enabled devices or phones, enabling features like contact tracing or social networking within a defined physical space.
GPS (Global Positioning System) / GNSS (Global Navigation Satellite Systems):
- Satellite-Based Positioning: Your phone's GPS receiver listens for signals from multiple satellites orbiting Earth. By precisely measuring the time it takes for these signals to arrive, your phone can calculate its exact latitude, longitude, and altitude.
- Assisted GPS (A-GPS): To speed up GPS acquisition and improve accuracy, especially in challenging environments, A-GPS uses cellular and Wi-Fi data to provide the GPS receiver with initial location estimates and satellite orbit data. While the core positioning is satellite-based, the assistance relies on other radio signals.
- App Permissions: Many apps request "Location Services" permission, granting them access to your GPS data. If granted, these apps can then transmit your location data to their servers, enabling a wide range of services but also creating privacy concerns if the data is misused or sold.
Near Field Communication (NFC) / Radio-Frequency Identification (RFID):
- Contactless Interactions: While typically short-range, NFC and RFID enable tap-to-pay, access control, and reading smart tags.
- Transactional Tracking: Every time you use your phone for a contactless payment or to scan an NFC tag, that action logs your presence at a specific location at a specific time. While not continuous tracking, it creates a digital breadcrumb trail that can infer your movements and habits.
It's clear our phones are constantly communicating, not always for our benefit. A good quality Faraday bag can quickly and easily end all those conversations.
Doesn't "Airplane Mode" Do The Same Thing?
Not really. Airplane mode is a convenient way to temporarily disconnect for airline safety or to save battery, but a Faraday bag provides a much more robust, physical barrier against all electromagnetic signals. This ensures a true "air gap" for privacy and security that software alone cannot guarantee. This is especially true if features like "Find My Phone" are enabled, as they can allow a device to remain a beacon for location, even when the phone is turned off. "Find My Phone" is excellent for finding your device, but it sacrifices complete signal blackouts.
What Else Can a Faraday Bag Be Used For?
My initial thought was only about phones. However, the broader principle is this: if it communicates wirelessly, it can potentially be intercepted, tracked, or cloned. Considering the number of items that use radio frequencies, the bigger picture came into view.
Modern Car Keys (Key Fobs):
- The Problem: Key fobs for "keyless entry" and "push-to-start" vehicles rely on a constant, low-power radio signal. When you're near your car, the car detects this signal to unlock or start the engine. This signal can be "relayed."
- The Crime: Thieves use devices to amplify the key fob's signal from inside your home. One thief holds a receiver near your house, picking up the key's faint signal. That signal is then relayed to a second thief by your car, making the car "think" the key is present. The car unlocks and starts, allowing them to drive off in seconds.
- The Faraday Solution: Placing your key fob in a small Faraday sleeve completely blocks its signal. Relay devices won't detect anything, and your car remains secure. It's a simple, effective defense against this type of car theft.
Contactless Bank Cards (RFID/NFC Cards):
- The Problem: Credit and debit cards with the "tap-to-pay" symbol use RFID or NFC technology. While convenient, your card constantly emits a signal.
- The Crime: "Skimming" can occur when criminals with a portable RFID reader walk past you in a crowded place and wirelessly scan your card details from your wallet or pocket without touching you. They can then use this information for fraudulent purchases.
- The Faraday Solution: While many wallets now have RFID-blocking material, a Faraday sleeve provides a guaranteed shield. Placing your contactless cards inside a sleeve (or a wallet that fully incorporates Faraday technology) prevents these unauthorized scans.
Laptops and Tablets (especially when traveling):
- The Problem: Like phones, laptops and tablets have Wi-Fi, Bluetooth, and sometimes cellular radios. When you're traveling, especially in airports, cafes, or hotels, these devices constantly broadcast signals and are prime targets for hacking attempts or data interception via insecure public networks.
- The Crime: "Evil Twin" Wi-Fi attacks (where a hacker sets up a fake public Wi-Fi network), malware delivery, or sniffing unencrypted traffic on a network can compromise your device and steal sensitive information.
- The Faraday Solution: If you're working with highly sensitive data or need absolute assurance that your laptop isn't communicating wirelessly (even in sleep mode), placing it in a large Faraday bag provides an "air gap." This is crucial for journalists, business travelers, or anyone handling confidential information who needs to be certain their device isn't vulnerable to remote access or surveillance during transit.
Wearable Tech (Smartwatches, Fitness Trackers):
- The Problem: These devices collect a wealth of personal data: heart rate, sleep patterns, activity levels, and your location when paired with your phone. They communicate wirelessly via Bluetooth, Wi-Fi, or cellular.
- The Privacy Concern: This data, while useful, is often transmitted to company servers and can potentially be accessed by third parties or used for profiling. This isn't always a direct "crime," but it's about controlling who has access to your very personal health and movement data.
- The Faraday Solution: While impractical for daily wear, if you have sensitive data on a wearable and need to ensure it's not transmitting or updating, placing it in a Faraday sleeve can temporarily isolate it.
The common thread here is that wireless communication equals potential vulnerability. A Faraday sleeve doesn't make your device or card "invisible" forever, but it gives you a crucial physical "off switch" for all wireless signals. This allows you to control when and where your digital footprint is visible and accessible. It's a simple, non-digital tool for real-world privacy and security in a hyper-connected world. Just drop the item in the bag, close the top, and you're good to go. Even better, these bags come in a wide variety of sizes, features, and prices.
Which Bag Are You Using?
We've tried a few options and found the Mission Darkness Dry Shield Faraday Phone Sleeve from MOS Equipment best met our needs. It excels at blocking signals for a wide range of equipment and is also waterproof, which is helpful for protecting gear in rain or snow. However, the magnetic closure really sold us. Many bags use fabric closures, which are nice but can easily collect pet hair. The magnetic closure prevents that. These bags are also available in a wide array of sizes.
Final Thoughts
Writing this has given me a new appreciation for the protection a Faraday bag provides. Even if you're not worried about tracking, consider the digital detox it can provide by shutting off from the world for a few hours. Don't worry, all those messages and posts will still be there when you pull your device out. It's an inexpensive measure of peace you might consider adding to your own kit.
Remember, we may not have anything to hide, but everything to protect.
