USB data blockers

What USB data blockers are

• Many names: Also sold as USB condoms, charge-only adapters and charge-only cables.
• Adapter or cable: The protection either plugs onto the cable you already own or is built into a cable that has no data wires.
• Not a power blocker: PortaPow also sells the opposite: a USB power blocker that passes data and cuts the 5 V line, made for specialist uses such as some 3D printers.
• Who makes them: PortaPow in London, Plugable, StarTech, Afterplug and OffGrid all sell data blockers or charge-only cables.

How they still charge

With the data wires gone, a phone still has to learn how much current it may draw. Blockers answer with fixed signals or, on USB-C, keep the separate wire that negotiates power.

• The 500 mA default: Under the original USB rules a device starts at 100 mA and may rise to 500 mA only once configured over data, which a blocker never allows.
• Signals on the data pins: A dedicated charging port tells a device it may draw more by placing a resistance across D+ and D−; Apple chargers set voltages on those pins instead.
• Resistors, no chip: Plugable’s USB-MC1 puts resistors across the data lines for up to 1 A and argues that chips inside a blocker bring risks of their own.
• SmartCharge chip: PortaPow’s USB-A blocker carries a chip that switches between Apple, Samsung and universal signals so charging is not slowed.
• Power on its own wire: USB Power Delivery negotiates over the CC wire, not the data pairs, so a USB-C blocker or charge-only cable can keep it and pass up to 240 W.
• E-marker chips: USB-C cables built for more than 60 W must carry an eMarker that identifies them over the CC wire; Plugable’s 240 W charge-only cable has one.

Types

• USB-A adapters: A male-to-female plug for the USB-A ports on chargers, cars and computers; your own cable plugs into it.
• Pure, chip-free models: PortaPow’s Pure Data Blocker has a clear case and no electronics inside, so you can see it holds only power wires.
• USB-C inline blockers: Male-to-female USB-C pieces that pass Power Delivery for laptops; Afterplug rates its pair to 240 W.
• Device-side blockers: PortaPow’s USB-C version can sit between a station’s fixed cable and your phone, guarding against the cable as well as the port.
• Charge-only cables: Cables made with no data wires; Plugable says they leave no extra piece to carry, lose or forget.
• Retractable cables: Afterplug’s retractable USB-C data blocker cable locks at five lengths, from 6 in to 3.3 ft.
• Settings on the phone: Android 16’s Advanced Protection can cut USB data while the phone is locked; Samsung’s Auto Blocker stops commands sent over a USB cable.

What to look for

• Match your ports: Carry a USB-A blocker for A ports and a USB-C one for C ports; Afterplug warns its C blocker on a USB-A-to-C cable may charge slowly or not at all.
• Fast charging kept: Look for a smart chip on USB-A or Power Delivery on USB-C; Quick Charge and Samsung Adaptive Fast Charging need data and do not pass through.
• Laptop power: To charge a laptop, pick a USB-C blocker or cable rated for Power Delivery; the Extended Power Range reaches 240 W at 48 V and 5 A.
• Proof you can see: PortaPow cuts an inspection window to show the missing data wires and laser-etches NO DATA on the plug.
• Test it at home: Kaspersky advises plugging a charge-only cable into a trusted computer first and checking that no data-transfer prompt appears.
• Slim enough: PortaPow’s USB-A blocker has an 18 × 11 mm profile so it leaves the next port free; Afterplug’s USB-C model fits a phone with its case on.

On the plane and on the trip

• Seat-back ports: A reader review quoted by AFAR says a Kindle on a plane’s USB port drops into disk mode and cannot be read; through a blocker it charges and stays readable.
• Car ports: PortaPow says its blockers stop the sync pop-ups a car’s USB port triggers; another review quoted by AFAR kept Bluetooth connected that way.
• Your iPhone’s own guard: On USB-C iPhones, Settings › Privacy & Security › Wired Accessories offers Always Ask; a locked iPhone still charges from a USB power adapter.
• Update before you fly: Since iOS 18.4 and Android 15, a passcode or biometrics is needed to open USB data; Kaspersky found Samsung’s One UI 7 did not ask.
• Never tap Trust: An expert told TechRadar not to select Trust This Computer while charging; Symantec’s 2018 Trustjacking research showed that trust can carry on over Wi-Fi.
• Power bank as backup: TSA requires power banks in carry-on bags, never in checked bags.

Limits and care

• No proprietary fast charge: Qualcomm Quick Charge and Samsung adaptive fast charge need data, so a phone charges at standard speed; Kaspersky says the same of charge-only cables.
• Chip-free is slower: PortaPow says its chip-free Pure blocker can charge more slowly with some device and charger pairs; Plugable’s chip-free design allows up to 1 A.
• Power and nothing else: A full cut on the data lines also stops keyboards, flash drives and external displays, Android Authority notes.
• A blocker can be fake: Hak5 sells the O.MG UnBlocker, a red-team tool that looks and works like a data blocker while hiding a wireless implant.
• Fragile USB-C plugs: PortaPow makes its USB-C blocker a 15 cm cable because a long, thin USB-C adapter is more likely to break over time.
• Updates matter most: Kaspersky calls the latest iOS or Android version the most important protection of all.

A short history

• 2009: PortaPow, a London electronics maker founded in 2005, turns to data blockers.
• Late 2012: An NSA guide tells traveling government staff to charge only with their own cables overseas and to avoid public kiosks.
• July 2017: Estonia gives data block USB adaptors as official gifts of its EU Council presidency, to promote basic cyber hygiene.
• July 2018: iOS 11.4.1 adds USB Restricted Mode: an iPhone locked for an hour stops USB data but still charges from a power adapter.
• May 2021: USB-C’s Extended Power Range raises USB charging to 240 W.
• 2025: Android 16’s Advanced Protection mode can turn off USB data while the phone is locked.
• August 2025: Plugable launches 240 W USB-C charge-only cables in 6-inch, 1 m and 2 m lengths.