How SD Card Lock Works

Here is a video showing you where is the location of the lock on an SD Card. It is on the left side of the card and you lock the card by pushing it downward.

When the card is locked, you can only read from the card and you are not able to modify anything on it. It becomes a read-only access card.

What Is Inside SD and microSD Card

The video below shows the inside detail of an SD Card as well as a microSD Card. You can see that the lock switch at the left side of the SD Card is just a plastic slider. It does not interfere with the card’s internal electronics circuitry.

The function of a lock switch slider is to tell the card reader that, the SD Card can only be read and it is a write-protected card.

When an SD Card is in the camera, you can know whether the SD Card is locked or not, by taking a photo and seeing whether it can be saved.

If you can save the photo, you try to delete it. If you also can delete the photo, the SD Card is likely unlocked. However, if you cannot save the photo and are also not able to delete it, the SD Card is definitely locked.

How SD Card Reader Works

Most of us would have a couple of SD Cards with us and it will benefit us if we know how the SD Card reader access those data/files on our SD Cards.

To accept an SD Card into the card reader, you will need to have an SD Card slot inside the card reader. There will be pins on the top and bottom sides of the slot. Pins on the top will grip the SD Card when it is inserted into the slot. The bottom pins form the connections with those pins on the SD card for transferring the data.

Every SD card has 9 pins to exchange data within the card reader. The pin configuration is:

  • Data pins: Pin 1, 7, 8, 9
  • Ground pins: Pin 3, 6
  • Command pin: Pin 2
  • Clock pin: Pin 5
  • Voltage Input pin: Pin 4
adaf0d755833e9e293aa196a4d8eeacd cropped


There are 2 micro switches inside the card slot (switch 1 and 2). These micro switches are spring-loaded metal pins, which help to detect the lock switch’s position. When an unlocked SD card is inserted into the slot, the lock lifts up micro switch 1 allowing it to connect with the metallic casing. This in turn connects to the micro switch 2 and allows writing on the SD card.

e1f4abe9981abe83c85b1f542d7a7f82 cropped

                           2 micro switches inside the card slot to detect the lock switch on the SD card

For a locked SD card, micro switch 1 is placed near the lock switch therefore it is unable to make contact with the metallic casing. In this case, the 2 micro switches are not connected therefore the SD card is being protected and you will not be able to write anything on it.


Remove Write Protection On SD Card Without the Lock Switch

In case your SD Card Lock Switch has broken or missing, you can do the following steps to remove the Write protection on the card.

  1. For Macbook Computer
    1. Insert your SD Card into the card slot and click the file you want to protect
    2. Click “Get Info”
    3. Under the “General” section, remove the tick at “Locked”
    4. You will notice that the “Sharing & Permissions” section shows “You can read and write”
    5. This indicates that you can start writing data on your SD Card
  2. For Windows Computer
    1. Put the SD Card in the memory slot and click the file you wish to write-protect
    2. Right-click your mouse and select “Properties”
    3. Under the “General” section, look for the last row Attributes and remove the tick at the “Read-only” box
    4. Click “Apply”
    5. You can now write anything on the card

Final Thoughts

The lock switch at the left side of your SD Card helps to keep the content on your card safe. By toggling it to the lock position, it prevents data overwriting on it.

Although it is not foolproof to protect your files/data on it, it is an additional safety feature that all SD card manufacturers implement on their cards.

Whenever you encounter a Write-error message, do not panic. Take a look at the lock switch to see whether it is being locked, if yes just push it up to unlock the switch and you can continue to write data on it.

Want to know more about SD Card related information?

Check out some of our articles here:

Creating your own business online with step-by-step guide

We build this website using Siterubix's powerful platform. If you wish to learn about this, click on the RED button, and we will take you to the site.

Leave a Comment