You're back from a shoot, the card goes in, and nothing appears. Before anything else: if that card holds footage you haven't offloaded, don't format it, don't shoot on it again, and don't run any repair that writes to it. Every fix below is ordered so the ones that can't touch your files come first.
Most of the time the card is fine. Card readers fail constantly, the little lock switch gets nudged in a camera bag, and Finder hides external volumes by default on plenty of Macs.
TL;DR: Try a different reader or port first (readers fail more than cards), check the physical lock switch on the card's side, and check Finder → Settings → General shows external disks. If Disk Utility sees the card but it won't mount, run First Aid. If the card mounts anywhere at all, offload the footage before any further fixing. Never format a card with un-offloaded footage.
Start With the Reader, Not the Card
The cheap card reader is the most failure-prone object in the chain. Try:
- A different reader. If you have a camera cable, connecting the camera directly via USB also works as a cross-check (the camera reads the card with its own hardware).
- A different port, plugged straight into the Mac rather than through a hub.
- The built-in SD slot, if your Mac has one. Note the reverse too: built-in slots occasionally fail while USB readers keep working, so a card that stopped appearing in the slot isn't necessarily dead.
If the card reads in the camera but in no reader on your Mac, the card is almost certainly fine and your reader (or its cable) isn't. If nothing reads it, including the camera, skip to the recovery section.
Check the Lock Switch
Full-size SD cards have a physical slide switch on the left edge. Locked cards mount read-only, and a handful of readers refuse them entirely. Slide it toward the contacts (away from "LOCK") and reinsert. The switch moves with a light touch and gets nudged constantly inside camera bags. microSD cards in an SD adapter inherit the adapter's switch, so check the adapter too, and try a different adapter if you have one; adapters fail almost as often as readers.
Check Whether Finder Is Just Hiding It
Open Finder → Settings → General and make sure External disks is checked under "Show these items on the desktop," and the same under Settings → Sidebar → Locations. Cards mount like any external volume, and if external disks are hidden, the card can be mounted and working with nothing visible anywhere you'd normally look.
Look for the Card in Disk Utility
Open Disk Utility, and enable View → Show All Devices. Three outcomes:
The card appears, with its volume grayed out. Select the volume and click Mount. If it mounts: offload your footage now, before experimenting further.
The card appears but won't mount, or the volume is missing. Run First Aid on the volume. Camera-formatted cards are FAT32 or exFAT, and an interrupted write (battery died mid-shot, card pulled while the camera's buffer was flushing) leaves a dirty filesystem that First Aid usually repairs. If First Aid fails and the footage matters, stop here and go to recovery. Repeated repair attempts on a corrupted card can overwrite recoverable data.
The card doesn't appear at all. Check System Report → USB (Apple menu → About This Mac → More Info → System Report). If the reader appears there without the card, the card isn't answering electrically. Try the camera one more time; if the camera can't see it either, it's a physical card failure.
You can also check from the terminal, which sometimes surfaces a card that Disk Utility's refresh missed:
diskutil list external
If the Card Has Footage on It: Recovery, in the Right Order
The rule that protects you: recoverable data survives being read, not being written. Formatting, "fixing" prompts from Windows, camera re-initialization, and even shooting one more clip can overwrite the exact sectors your footage lives in.
If the card mounts but files are missing or folders look scrambled, or the card won't mount but is electrically alive, recovery software (PhotoRec is free and open source; several paid tools are more comfortable to use) reads the raw card and carves out image and video files. Recover to your Mac or an external drive, never to the card itself.
If the card is electrically dead, no software can help; professional recovery labs can sometimes read the flash chips directly, at a price only worth paying for irreplaceable footage.
And if the camera shows the clips but the Mac never sees the card properly, remember the camera-as-reader trick above: pull footage over the camera's USB connection and treat the card as suspect afterward.
After the Scare: Make the Next Card Failure Boring
A card that fails after offload is an annoyance. A card that fails before offload is a lost shoot. The difference is entirely about when the copy happens, which is why the offload should be the first thing after any shoot, and why it should land on more than one destination.
Tusk is a Mac app that automatically backs up your project folders to multiple locations and tracks where every file lives — even when your drives aren't connected.
Tusk's offload does this in one pass: plug in the card, pick your backup destinations (external drives, cloud, or both), and it streams the footage to all of them simultaneously, reading the card exactly once, with a BLAKE3 checksum verifying every file on every destination. One card read matters more than it sounds; a card that's starting to fail often survives one full read but not three. When the offload finishes verified, formatting the card in the camera is a decision, not a gamble.
The SD card offload guide covers the workflow, and the OffShoot vs ShotPut Pro vs Silverstack comparison covers the dedicated offload tools if you're choosing between them.
FAQ
Most commonly: a failed or incompatible card reader (try a different one, or connect the camera by USB), the card's physical lock switch got nudged, Finder is set to hide external disks, or the card's filesystem was corrupted by an interrupted write and needs First Aid in Disk Utility. Actual dead cards are the least common cause. If the card holds un-offloaded footage, avoid any fix that writes to the card until the footage is copied off.
First check Finder → Settings → General and Sidebar to confirm external disks are shown at all. If they are, the volume probably isn't mounted: select it in Disk Utility and click Mount. If mounting fails, run First Aid on the volume; camera cards use FAT32 or exFAT and an interrupted write commonly leaves them unmountable until repaired.
The camera is proof the card works, so the problem is in the reader chain: the reader, its cable, a hub, or an SD adapter around a microSD card. Swap each one. As a workaround, connect the camera itself over USB and copy the footage that way. Some cameras expose the card as a plain volume; others need their transfer app, but either route gets the footage off a card your readers can't see.
Stop writing to the card immediately: no formatting, no new shots, no repair prompts from other devices. If the card mounts or is at least detected, recovery software (PhotoRec is free; paid tools are easier to use) reads the raw card and extracts image and video files. Always recover to a different drive, never back onto the card. If the card isn't detected anywhere, including the camera, only a professional recovery lab can help.
Only after the footage is offloaded and verified somewhere else, and then only in the camera, not the Mac. In-camera formatting lays down exactly the filesystem the camera expects. That said, a card that has corrupted once is telling you something: use it as a backup card, not the primary for anything important. Cards are the cheapest component in the entire chain and the only one holding unreplaceable data between shoot and offload.
Copy to at least two destinations with checksum verification before formatting the card. Dedicated offload tools (OffShoot, ShotPut Pro) and Tusk all verify every file against a checksum after copying, which catches silent transfer corruption that a plain Finder drag can't. Tusk fans out to multiple destinations in a single read of the card, which is gentler on aging cards and confirms every copy is intact before you touch the format button.