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01OTG in one paragraph
USB OTG is a feature that lets a phone switch from being a USB device to being a USB host. Normally your phone is the thing that plugs into a computer. With OTG, the phone becomes the computer, and flash drives, keyboards, card readers and microphones plug into it.
The name dates from the Micro-USB era, when you needed a special OTG cable to tell the phone to switch roles. USB-C made the switch automatic: the port works out which side is the host when you connect. So on a modern phone, OTG mostly means "the port works both ways" and the only thing you might need is an adapter to fit an older, rectangular USB-A plug.
Apple doesn't use the term, but USB-C iPhones support the same idea. You can open files from a USB drive in the Files app, type on a wired keyboard, or import photos straight from a camera. Lightning iPhones could do some of this through Apple's camera adapters.
02What you can plug in, and what works
| Accessory | Android | USB-C iPhone | Watch out for |
|---|---|---|---|
| USB flash drive | Yes, in Files or My Files | Yes, in the Files app | Format it exFAT to read it everywhere |
| SD / microSD card reader | Yes | Yes, and Photos can import | Cheap readers can be slow with big video files |
| Portable SSD | Usually | Yes; Pro models transfer fastest | Needs enough power; some need a hub |
| Spinning hard drive | Often fails | Often fails | Draws more power than a phone supplies |
| Keyboard | Yes | Yes | Wireless keyboards with USB receivers usually work too |
| Mouse | Yes, shows a cursor | Through AssistiveTouch | On iPhone, set it up in Accessibility settings |
| USB microphone | Most class-compliant mics | Most class-compliant mics | App support varies |
| Wired game controller | Many work | Some work | Bluetooth is often simpler |
| Ethernet adapter | Many work | Yes | Handy in hotels or for a stable stream |
One more trick: a USB-C to USB-C cable between your phone and a pair of earbuds or a watch charger lets the phone charge them. It's slow, but it saves a dead pair of AirPods on a flight.
03Getting a USB accessory to connect
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Get the right adapter
For a USB-A flash drive or keyboard, use a USB-C male to USB-A female adapter. The phone end is the male USB-C plug; the accessory plugs into the full-size socket. Adapters going the other way are for plugging a USB-C cable into an older laptop, and won't help here.
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Open the phone with your passcode first
iPhones block new USB accessories while locked for security, and may ask you to allow the accessory. Enter your passcode or use Face ID, plug in, and tap Allow if prompted.
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Turn on OTG if your phone has a switch
Samsung, Google and Apple phones connect automatically. Some brands, including OnePlus and Oppo, have an OTG toggle in their additional settings that turns itself off after a period of inactivity. Search "OTG" in Settings.
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Open the right app
On Android, look in Files by Google or Samsung's My Files under USB storage. On iPhone, open Files, tap Browse, and the drive appears under Locations.
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Eject before you unplug
Android has an Eject option in the notification or Files app. On iPhone, finish any copy in progress before you pull the drive. Yanking a drive mid-write can corrupt it.
Most of the time it's the format. Phones read FAT32 and exFAT reliably; a drive formatted NTFS on Windows may not appear. Reformat to exFAT on a computer (this erases it) and it'll work on Android, iPhone, Mac and Windows.
04The power limit nobody mentions
When your phone is the host, it also has to power the accessory. Phones supply only a small amount. Apple lists 4.5W for accessories on USB-C iPhones, and Android phones are in a similar range. A flash drive, keyboard or card reader needs far less. A portable hard drive with spinning platters can need more, which is why it clicks, spins up and vanishes.
- Flash drives, card readers, keyboards, mice: run fine on phone power.
- Portable SSDs: usually fine, but some larger ones drop out under heavy writes.
- Hard drives, ring lights, multiple devices at once: use a USB-C hub with its own power input.
- Battery drain: anything plugged in draws from your phone. Unplug when you're done.
A hub with USB-C power pass-through solves both problems. Plug a charger into the hub, the hub into the phone, and accessories into the hub. The phone charges while it runs the gear. For streaming setups with a mic and light, see our creator phone setup.
05Adapters worth keeping in your bag
A couple of small adapters cover most OTG jobs. Keep a USB-C to USB-A adapter on your keyring for flash drives, and a card reader if you shoot on a camera or drone.
USB-C male to USB-A female adapters for drives and keyboards, and a USB-C card reader for SD and microSD.
For big file transfers, the cable matters as much as the drive. Charging cables usually run at USB 2 speed. A 10Gbps cable is the one to use with an SSD; our USB-C cable types guide explains the labels, and Lightning vs USB-C covers which iPhones can use the extra speed.
Questions people ask
How do I know if my phone supports OTG?
If it has a USB-C port and was made in the last several years, it almost certainly does. The quickest test is to plug in a flash drive with an adapter and look for it in your Files app. Some Android brands need an OTG switch turned on in Settings first.
Does the iPhone support USB OTG?
USB-C iPhones (iPhone 15 and later) support external drives, keyboards, card readers, mics and cameras directly. Apple just doesn't use the OTG name. Lightning iPhones need Apple's Lightning to USB camera adapter for similar jobs.
Can I charge my phone while using an OTG device?
Not with a simple adapter, since it uses the only port. You need a USB-C hub with power pass-through: plug the charger into the hub and the accessory into one of its ports.
Why does my external hard drive not work on my phone?
Usually power. Spinning hard drives can need more than a phone's port supplies. Try a USB-C hub with its own power input. If the drive lights up but doesn't appear, reformat it to exFAT.
Is an OTG cable different from a normal cable?
For Micro-USB phones, yes: an OTG cable had a wiring change that told the phone to act as host. With USB-C the phone figures it out automatically, so any proper USB-C adapter or cable works.