Owners of Xiaomi Redmi 9 smartphones sometimes face an unexpected situation: after updating the system or accidentally touching the settings in the top of the screen, a strange icon resembling the letter “T” or the acronym TTY appears. For most users, this symbol becomes a complete mystery, causing concern about a possible virus or a malfunction of the MIUI operating system.
In fact, it's a standard accessibility feature that was built into mobile phones long before the advent of modern smartphones, designed for people with hearing or speech impairments, allowing them to exchange text messages during a voice call. However, for the average Redmi 9 user, activating this option can bring more problems than benefits, including unstable communication.
In this article, we will discuss in detail what is behind the term “teletype”, why this feature could turn on on its own on your device and how to safely deactivate it. Understanding the work of system services allows you to better control your gadget and avoid unnecessary resource consumption.
What is hidden behind the acronym TTY
The term teletype comes from the English Teletypewriter, which literally means "teletype." Historically, this device was used to transmit printed text over telephone lines. In the context of modern smartphones, including the Xiaomi Redmi 9, it is a software emulator that converts voice signals into text and vice versa in real time.
The main purpose of this technology in mobile OS is accessibility, people with disabilities can have a full dialogue using special external devices or screen interfaces without relying on hearing, the system encodes sounds into tonal signals that are decoded on the other side.
⚠️ Warning: A constantly active teletype mode may block the ability to make regular voice calls if the interlocutor does not support this technology or does not have compatible equipment.
It is important to understand that the regime TTY — It's not an application, it's not a virus, it's a deep system setup that affects the modem and the audio processor, and when activated, it goes into a special standby mode that can conflict with modern VoLTE protocols or HD-ring-off.
Why you need a function and who is useful to it
Although few people use teletypes as they are in the classic sense in 2026, the feature remains an important part of communication standards, primarily critical for hearing-impaired people, enabling them to use emergency services and communicate with loved ones.
In some countries, having a working TTY mode is a requirement for mobile device certification, which is why manufacturers like Xiaomi leave this option in the firmware, even if it is hidden from the average user in the standard settings menu.
- 📞 Allows text to be transmitted during a voice call without interrupting the connection.
- 🆘 Provides access to rescue services for deaf subscribers.
- 📝 Converts incoming voice to text stream on the screen.
For a Redmi 9 owner who has no medical indications, this feature is almost useless, and its work requires additional processing power to encode and decode signals, which in theory may have little impact on battery autonomy.
Historical background
Why TTY is on Redmi 9 on its own
Often people ask, "I didn't touch anything, where did this setup come from?" In fact, random switching on is rare, most often because of the specifics of the MIUI shell or updating the basic programs.
One common reason is to reset your network settings or update your firmware. In the process of migrating data, the system can restore old configuration files that had teletype mode activated, and this can also happen when you install some applications for calling from third-party sources.
There's also the human factor, and the special feature menu is sometimes hidden in the depth of the settings, but if you use the Quick Commands feature or the Google Assistant voice assistant, you can accidentally activate the switch you want, especially when the phone is in your pocket or bag and the screen responds to touch.
⚠️ Attention: If the icon TTY It's gone and it's gone, but it's gone, and it's gone, and it's got a little bit worse, so check if Safe Mode is on. It's different, but it can manifest in a similar way to an inexperienced user.
Sometimes activation occurs after a visit to a service center, wizards can turn on diagnostic modes to check the speaker and microphone, forgetting to return the settings to their original state, in which case, turning off the TTY becomes the owner's task.
Teletype Impact on Communication Quality and Battery
Teletype mode imposes certain limitations on communication quality, and as the channel is reconfigured to transmit tonal signals, voice quality can deteriorate, echo or delay, and in poor network coverage, Redmi 9 can lose signal altogether.
In terms of power consumption, the constant processing of the audio stream to convert to text requires the work of the processor. Although modern MediaTek chips installed in Redmi 9 are quite energy efficient, background activity of the modem in non-standard mode can lead to faster discharge.
| Parameter | TTY mode is off. | TTY mode on |
|---|---|---|
| Voice quality | High (HD) | Medium/Low |
| Battery consumption | Standard. | Elevated |
| Connection speed | Instant. | Possible delay |
| Compatibility | Complete. | Only with TTY support |
It is also worth noting the problem of compatibility with networks. 4G and 5G. Not all operators handle calls with activated teletype correctly on new generation networks, which can lead to a call reset or switch to a slower standard. 2G/3G.
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For the average user, active TTY mode is a source of potential communication problems and unnecessary charge consumption without any practical benefit.
How to turn off teletype via the engineering menu
Unlike some other brands, the standard Xiaomi Settings menu often doesn’t have a TTY switch, hidden in the engineering menu or testing menu, and requires you to enter a special code to access it.
Open the standard Phone app you use to dial. Enter the combination ##4636##. Once the last star is entered, the hidden Testing menu will automatically open. If this does not happen, your operator or firmware can block this code.
In the list that opens, select Phone Information. Scroll down to Set up your preferred network type or Set your preferred network type. There you will find a drop-down list where the current TTY mode can be specified.
☑️ Shutdown algorithm TTY
You need to find the TTY Mode option. Click on it and select "TTY Off." This action instantly deactivates the function. If there is no such item in the list, then your version of MIUI has closed access to this setting and you will need to use third-party applications.
Alternative methods and applications
If the engineering menu didn’t work or the code didn’t work, you can use third-party utilities.There are apps built specifically to manage hidden Android features like TTY on the Google Play store.
One popular solution is the TTY Mode app, which adds a handy switch to the settings or notification bar once installed, allowing you to quickly turn the function on and off without entering complex codes.
- 📱 Download the management application TTY reliable.
- 🔐 Provide the necessary permissions to change system settings.
- ⚙️ Switch the slider to the "Off" position".
You can also try resetting your network settings. Go to Settings → About Phone → Reset and select Reset your Wi-Fi, Mobile Internet and Bluetooth settings. This will return all network settings, including TTY, to factory values where they are normally disabled.
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Before making changes to the engineering menu, take a screenshot of the current settings, which will help you get back to the way it was if something goes wrong.