How to appoint SIM-Default card on Xiaomi Redmi 9: full instruction

Why it is important to set up correctly SIM-maps on Redmi 9

Xiaomi Redmi 9 supports the work with two SIM-By using cards, which allow you to separate personal and work numbers, use advantageous rates of different operators or keep in touch in roaming. SIM-Default cards you risk sending SMS Spending money on expensive mobile Internet or skipping important calls is a particularly pressing problem for users who often switch between cards or use the device when traveling.

In this article, we’ll look at not only basic settings, but also nuances that are not covered in the standard instructions, such as how to tie a particular SIM to a specific contact, why settings are sometimes reset after a MIUI update, and what to do if the phone doesn’t see one of the cards, and how to optimize battery consumption when working with two SIMs and avoid conflicts between operators.

Note that the Redmi 9’s routine (including Redmi 9A, 9C, 9T) may vary slightly depending on the firmware version. We’ll focus on current MIUI 12/13/14 builds, but we’ll provide alternative paths for older versions.

Preparation: compatibility check SIM-map

Before you set up SIM-Default cards, make sure both cards are correctly recognized by the system. Redmi 9 supports combinations:

• 📱 Two nano-SIMs (4FF)
• 📱 One nano-SIM + microSD card (in a hybrid slot)

If your phone doesn’t see one of the SIMs, follow these steps:

1. Remove and re-insert the card, making sure the contacts are clean and not bent.
2. Check if the operator has activated the SIM (sometimes a hotline call is required).
3. Reboot the device – slot initialization is sometimes lost in MIUI.

Please note: if you are using a hybrid slot, priority is given to the slot. SIM-The memory card will not be available in this case, and some operators (e.g., the card) will be disabled, Tele2 Or Yota may require additional settings. APN for the proper operation of the Internet.

⚠️ Note: If after installation of the second SIM The phone stopped catching the network on the main map, check if operators are conflicting over frequency bands. For example, MTS and Beeline in some regions use the same bands. 4G, This can lead to the “hang” of the communication module.

Step-by-step: SIM assignment by default

Let's move on to the main process. SIM-default card, SMS and mobile Internet:

1. Open the Settings app (the gear icon on the desktop).
2. Go to section. SIM-maps and mobile networks (in some firmware - Double SIM mobile).
3. Select the Settings item SIM-map.
4. Press the line. SIM-default-card.

Three options will be available to you:

• 📞 Calls: Choose SIM For outgoing calls (you can leave to ask always).
• 💬 SMS: Specify a card for sending messages.
• 🌐 Mobile data: select SIM Internet (important for tariffs with unlimited traffic).

If you want your phone to ask you which SIM to use for a call or SMS every time, choose the Ask Always option. This is convenient if you switch between numbers often. For mobile Internet, there is no such option - there is always one card selected.

Additional settings: linking SIM to contacts

Few people know, but in Redmi 9 you can appoint an individual SIM-It's useful if you call your colleagues from your work number and your friends from your personal number:

1. Open the Contacts app.
2. Select the contact you want and click Edit (pencil icon).
3. Slip it on the field with the phone number.
4. In the menu that appears, select SIM-Default card and specify the desired.

Now, when you call that contact, the phone will automatically use the SIM attached, and you can also configure SMS.

Another useful trick is that if you often call the same operator's numbers (like MegaFon), you can set up the redirect rules.

1. Go to Settings. → SIM-maps and mobile networks → Call forwarding.
2. Select the SIM you want to set the rule for.
3. Specify the terms (e.g., “if the number is unavailable”) and the number for forwarding.

Solving the Problem: Why Settings Are Straying

Redmi 9 users sometimes experience SIM default settings reset after an update or reboot.

If the problem persists, try resetting the network settings (as in the table above) or reset to factory settings with data storage.

⚠️ Note: Some custom firmware (such as LineageOS or Pixel Experience) has dual settings. SIM It may not work properly, and in this case we recommend returning to the official MIUI or use specialized patches from the community.

Optimizing the two SIMs: Tips for saving battery life

Use of the two SIM-The card can increase battery consumption by 10 to 15 percent, as the phone is constantly scanning the networks of two operators:

• 🔋 Turn it off. 4G second SIM, If it is used only for calls: Settings → SIM-map → [choose SIM] → Preferred type of network → 3G.
• 🔋 Enable the option to save traffic in the mobile network settings.
• 🔋 If one of them SIM It is rarely used, turn off the background data transmission for it.

Important: Redmi 9 with MIUI 12.5 and later has a hidden function called “Dual SIM Optimization” that automatically disables network scanning on an inactive card. To activate it, type ##4636## in the Phone app and select “Phone Information” → “Network Selection” → “Disable Unused SIM.”

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If you travel frequently, create separate roaming profiles in SIM settings. For example, you can turn off roaming data for one card, and leave only 2G for saving.

Also note the energy saving regime. MIUI It may limit background activity. SIM-To avoid this, add the Phone app to the exclusion list:

1. Go to Settings → Battery and Performance → Battery Consumption Management.
2. Select the Applications Selection.
3. Find the phone and install it without restrictions.

Frequent Mistakes and How to Avoid Them

When you set up SIM-Redmi 9 card users often make the following mistakes:

1. Ignore APN notifications. If you get a message after you set up your SIM, don't put it off. Without the right APNs, your mobile data won't work.
2. When changing the default SIM for the Internet, make sure that there is enough money or no-limit active.
3. Older versions of MIUI (below 12.0) may have dual SIM bugs patched in new builds.

Another common problem is conflict. USSD-If you're trying to send a team USSD-request (e.g. *100#) and the phone is using the wrong SIM, The crew will not reach the operator, so to avoid this, before sending it. USSD manually select the right one SIM dial-room.

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Always check which SIM is active for mobile data before roaming. Some operators automatically connect paid options when using the Internet abroad.

FAQ: Answers to popular questions