How to assign a default SIM card to Xiaomi Redmi: the complete guide

Owners of modern smartphones Xiaomi and Redmi often face the need to use two numbers at the same time, which makes the question of competent setting of communication priorities extremely urgent. The correct configuration allows you to flexibly manage communication costs and mobile Internet quality, without switching manually to the menu every time. MIUI system and the new HyperOS offer a wide range of tools for personalizing the work of communication modules, but it is difficult for beginners to understand the abundance of options.

In this article, we will discuss in detail how to assign a SIM card by default for various use cases, from standard voice calls to data transfer in the background. You will learn about the intricacies of working with shell settings, which are hidden from the surface, but are critical for the stable operation of the device. Proper distribution of roles between slots will help to extend battery life and avoid unnecessary write-offs.

Many users mistakenly believe that installing a SIM card in a particular slot automatically dictates the system's priorities, but this is not the case. The software allows you to completely ignore the physical location of the chips, assigning the main role of any of the installed cards.

Basic principles of working with two SIM cards in MIUI

The operating system developed by Xiaomi is based on Android, but has a deeply redesigned interface for managing network connections. Unlike stock Android, where settings can be scattered, everything is concentrated in a single logical unit, which makes life easier for the user, allowing you to quickly change the parameters of the network without long searches.

The key feature is that you can independently customize your profiles for different tasks, so you can use one SIM exclusively for voice and the other for packet traffic, or you can distribute the load differently, and the system remembers your preferences for each application separately, which creates an additional level of comfort.

⚠️ Note: When changing the main SIM card for mobile Internet, the active data session may be interrupted for several seconds while the module is rebuilt to a new frequency.

It’s important to understand that in modern Redmi models, both slots support 4G LTE and 5G standards, but they can’t work at the same time at maximum speed. Usually one card runs in high-speed data, and the second goes to standby mode or 2G/3G for receiving calls. This technology is called DSDS (Dual SIM Dual Standby).

Step-by-step: Selecting a SIM for calls and messages

To change the priority number from which outgoing calls will be made, you need to go to the appropriate settings menu. the interface may vary slightly depending on the firmware version, but the logic remains the same for all devices of the brand. First, open the main menu and find the Settings icon, then go to the section. SIM-maps and mobile networks.

In the window that opens, you will see a list of installed cards with their names and operator logos. The system will prompt you to select your preferred default card for several action categories. You need to find the Voice Calls item and click on it to reveal the list of available options.

There are three basic ways to make a call: you can hard-fix one SIM, choose a second one, or leave Always Ask, the latter is convenient for those who often forget which card is more profitable to call at a particular time, since the smartphone will request confirmation before each dial.

In the same way, the sending is configured SMS-If you use one SIM for charging messages (e.g., bank or service) and another for personal communication, it makes sense to assign a personal card to priority, which will prevent the accidental sending of paid commands from the wrong number.

Setting the priority of mobile Internet and data transfer

The most important option for an active smartphone user is choosing a data card, which determines which account will be debited from megabytes or gigabytes of traffic, and an error in choosing can lead to unexpected costs if the main SIM is not connected to a batch tariff.

To switch, look at the menu. SIM-The card and mobile network are the Internet or the data transfer point, and here the system will show the current active card, and by clicking on it, you can instantly switch the high-speed channel to another slot, and the changes will take effect immediately, without having to restart the device.

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Use the “Traffic Limit” function in the settings so that the system automatically turns off mobile Internet when you reach the established threshold, preventing you from going into deep minus.

It's worth noting that when you switch the Internet to a card that's in the bad reception zone, the speed can drop. MIUI sometimes suggests switching to a more stable network if it detects a significant difference in signal quality between the two operators, a smart feature that can be disabled in advanced settings.

If you travel frequently or move between carriers, it makes sense to set up a smart switch. Some firmware versions have an option to automatically switch the internet to a second SIM if the first one is completely lost, which ensures that you stay online.

Flexible settings for individual applications and contacts

Hard-wired SIM card binding for all tasks is not always convenient. Fortunately, Xiaomi shell allows you to reset system settings for specific cases. For example, you can set the phone so that messengers work through one SIM and the navigator through another, although technically the Internet is still taken from the main channel.

More interesting is the SIM selection feature when you call a particular contact. When you open a subscriber card in a phone book, there's often a small arrow or SIM icon next to the call button, and you can click on it and choose which number to call that person from, ignoring the global default settings.

• 📞 Favourite contacts: For frequently called numbers, you can remember the choice of SIM so you don’t switch manually every time.
• 🌐 Caller apps: Some third-party calling apps (VoIPs) may have their own network selection settings that prioritize system-based applications.
• 💬 Messengers: WhatsApp and Telegram are linked to the number when registering, but for calls through them, an active Internet channel is used, selected in the main settings.

You can also customize your incoming calls, and you can disallow incoming calls to one of your SIM cards at certain times of the day using Do Not Disturb mode or special profiles, especially for those who don't want to be distracted by work calls on weekends.

Table of comparison of modes of operation of SIM cards

To better understand the differences between modes of operation, let’s look at them in a comparative table, which will help you choose the optimal configuration for your needs.

And you can see from the table that separating roles allows you to optimize your energy consumption, so when one card is actively exchanging data, the other card goes into energy-efficient standby, which is an important aspect that is often overlooked when complaining about fast discharge.

Always Ask Mode, despite its flexibility, can be annoying when you use your phone actively. If you call different people often, constant pop-ups can slow communication.

Problem Solving: When the settings are not saved

Sometimes users are faced with a situation where after a reboot or update of the system, the settings are reset, and the phone starts using the wrong SIM again.

The first thing you need to do is check for system updates. Often these bugs are patched with security patches. Go to Settings → About Phone → MIUI version and check for a new version. If the system is up to date, try resetting the network settings.

⚠️ Note: Resetting your network settings will delete saved Wi-Fi passwords and Bluetooth pairs, but will not affect your personal files, contacts or apps.

To reset, go to Settings → Connection & Sharing → Reset Wi-Fi, mobile networks and Bluetooth. After this operation, the phone will reboot and you will have to re-enter Wi-Fi passwords, but problems with choosing a SIM card are often solved by this method.

If the problem persists, it may be the physical contact group of the slot, try to remove the SIM cards, wipe the chip contacts with soft dry cloth and insert them again, making sure they sit tightly in the tray. Sometimes oxidation of the contacts leads to the system not being able to correctly identify priority.

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If software methods do not help, try swapping SIM cards for slots – sometimes this forcefully updates the connection profile in the system.

Optimizing battery consumption with two SIM cards

Using two active SIM cards inevitably increases power consumption, as the radio module must communicate with two base stations simultaneously.

If the second SIM card is only used for rare incoming calls, it makes sense to turn off mobile Internet and limit background activity. Each SIM card has a 4G switch in its settings, which can be turned off for a secondary card, leaving only 2G/3G for voice communication, which will significantly reduce power consumption.

• 🔋 Background: Limit background activity of apps for the second SIM card in battery settings.
• 📶 Network search: if you're in an area where one of the carriers is not picking up the signal, the phone will constantly try to find the network, consuming the charge.
• 🌙 Sleep mode: Use a SIM card on/off schedule if such a feature is available in your firmware version to turn off unnecessary numbers overnight.

Also worth mentioning is the Smart 5G feature, which automatically switches communication standards based on load, which helps save charge.

To sum up, the flexible setting of the Xiaomi Redmi SIM card is a powerful tool for managing digital life. By properly allocating roles between numbers, you will ensure stable communication, cost control and optimal device life on a single charge. Don’t be afraid to experiment with settings to find the perfect balance for your use case.