Many Xiaomi smartphone owners who are closely studying their device’s settings may encounter a mysterious menu item called Teletype or Teletype (TTY), which is often hidden in the depths of engineering menus or special features settings, causing confusion among the average user: What is this feature, why was it introduced in Android and is it relevant to modern communications?
In fact, teletype is a technology that goes back to the middle. XX It was designed to send text messages over telephone lines, originally designed for people with hearing or speech impairments, allowing them to communicate at a distance without having to say words. In modern Xiaomi smartphones, such as the Redmi Note or Xiaomi Mi, this feature is emulated software, but its practical value for most users today is minimal.
If you accidentally activate this mode, your phone may stop making normal voice calls or start behaving outside the box when making calls. TTY-The mode will help you avoid communication problems and properly configure the device to suit your needs. In this article, we will discuss in detail the history of the technology, how to activate and deactivate, and the effect of this feature on the operation of your gadget.
What is the Teletype mode and its history
Teletype technology, known as Teletypewriter (TTY), or sometimes Telecommunication Device for the Deaf (TDD), came long before the digital smartphone era: in the middle of the last century, these were bulky typewriters connected to a telephone line that allowed text to be transmitted instead of voice. With the advent of mobile phones, engineers integrated support for this protocol into operating systems, including Android, which runs the MIUI and HyperOS shells.
The idea is to encode text characters into audio signals of a certain frequency that are transmitted over a voice channel. On the receiving side, the device decodes these signals back into text, displaying the message on the screen. For people with disabilities, this was a revolutionary breakthrough that allowed full use of telephone communication.
Today, the classic teletype is almost replaced by more modern solutions such as subtitled video calls, instant messengers and emergency response services. However, since accessibility standards require support for legacy functions, the option remains in the Android system code. It is important for users to know that enabling TTY mode can limit the functionality of a conventional voice call, switching the phone to a specific modem modem modem.
⚠️ Note: Activating teletype mode on some Xiaomi models may make it impossible to make normal voice calls before the feature is turned off.
Why you need TTY function in a modern smartphone
The main purpose of the teletype function in 2026-2026 is to ensure that the environment is accessible to people with hearing and speech impairments. If a user can not hear the interlocutor or talk, he can type text that will be sent as an audio signal, or read text received from the interlocutor. In Xiaomi and Poco smartphones, this is implemented through the built-in Phone application and system settings.
In addition, there are specific use cases, such as those in regions with unstable voice coverage, where text transmission over voice may be more reliable, although this is rather an exception, and the mode may be required when connecting to specialized corporate or government communication systems that still use TTY protocols to encrypt or transmit service messages.
For the average user with no special needs, this feature is a hidden reserve. Its presence on the menu does not mean that it should be used. On the contrary, the presence of active TTY modes can affect the speed of establishing a connection and the quality of voice communication in 2G/3G networks. So understanding why you need TTY helps to avoid accidental activation that can disrupt your communication.
- 📞 Providing telephone service for people with hearing and speech impairments.
- 📟 Compatibility with older emergency services systems in some countries.
- ⚙️ Technical possibility of text data transmission via voice channel.
- 🔒 Use in specific corporate networks with a closed protocol.
Types of teletype modes in Xiaomi settings
Xiaomi’s smartphone settings menu typically features several options for teletype. The specific mode you choose depends on what hardware is connected to your phone and what tasks you’re solving. The standard Android, installed on Redmi or Black Shark, offers the following basic options, each with its own features.
The first option is TTY Off, which is standard for 99 percent of users, and in this mode, the phone works like a normal voice communication device, using the full range of frequencies to transmit voice, and no text protocols are embedded in the voice stream, which ensures maximum sound quality.
Other modes are designed for specialized equipment. For example, TTY Full allows you to send and receive only text, completely disabling voice transmission. TTY HCO (Hearing Carry Over) mode allows you to hear the voice of the interlocutor, but respond with text. Conversely, TTY VCO (Voice Carry Over) allows you to speak with voice, but receive answers in text. Choosing the wrong mode will lead to the fact that you either do not hear the interlocutor or he will not hear you.
⚠️ Attention: Switching between modes TTY Full, HCO and VCO requires restarting the phone app or the smartphone itself to properly apply network settings.
To understand the differences will help the following table:
| Regime. | Voice (Incoming) | Voice (Outgoing) | Text |
|---|---|---|---|
| TTY Off | There is. | There is. | No. |
| TTY Full | No. | No. | There is. |
| TTY HCO | There is. | No. | There is. |
| TTY VCO | No. | There is. | There is. |
How to Enable and Configure Teletype on Xiaomi
In modern versions of the MIUI and HyperOS shell, the path to teletype settings can be hidden, as Xiaomi developers try not to overload the interface with rarely used features. However, if a feature is required, it can be activated through the standard Android settings menu.
Inside the phone app settings, look for Accounts and Calls or Additional Settings, and that’s where the Teletype Mode option often hides (TTY). If this item is not in the graphical interface, which is often found in global versions of firmware for Russia and the CIS, activation is possible only through the engineering menu or the Internet. ADB-This is done specifically to ensure that ordinary users do not change critical parameters of communication.
For advanced users, there is a way to activate via a hidden menu, you need to open the Phone app and enter a special code, for example, ##4636#. In the test menu that opens, you need to select Phone Information and find the switch. TTY. You can also use it. ADB-forced-inclusion:
adb shell settings put global tty_mode 1☑️ Pre-insertion check TTY
TTY’s impact on communication quality and battery
Teletype activation has a direct impact on the smartphone's radio module. Because tonal signals are used to transmit text, which occupy part of the voice channel's frequency range, the sound quality can deteriorate. In TTY Full mode, the voice communication is completely turned off, and the phone functions as a text terminal, which means that you can't hear the horns or the operator's voice.
In addition, the constant processing of teletype signals can lead to increased battery consumption. the processor is forced to constantly encode and decode data in real time, which puts additional strain on the system. On older Xiaomi models with capacious but worn-out batteries, this can be a noticeable factor, and delays in establishing a connection are also possible, since the networks must agree on a transmission protocol.
If you notice that the phone has started to behave strangely during calls (sound disappears, interference appears, calls are reset), check the status of the teletype. In most cases, the problem is solved by returning to the standard TTY Off mode. Modern 4G (VoLTE) and 5G networks have their own text transfer mechanisms (RCS), which work more efficiently and do not require legacy modes.
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If after turning on TTY, the sound in the speakers disappeared, check if the phone has switched to headset mode, since some external teletypes are connected through the headphone jack or Bluetooth.
How to turn off teletype and troubleshoot problems
If you accidentally enabled a teletype or the function was activated by a virus/failure, it must be disabled to restore normal operation. The easiest way is to go back to the settings of the Phone application and select TTY Off. If the menu is not available or the settings are not saved, you can use the network settings reset.
To reset network settings on Xiaomi, go to Settings → Connection & Sharing → Reset Wi-Fi, Cellular Networks and Bluetooth. This action will remove stored Wi-Fi passwords and Bluetooth settings, but return call settings to factory values, guaranteed to disable TTY. Once rebooted, the phone will work in standard mode.
In cases where software shutdown is not possible (for example, due to operator lock or damage to system files), a complete reset of the device may be required. ADB forcing a change in parameter:
adb shell settings put global tty_mode 0⚠️ Attention: Resetting network settings will delete all stored Wi-Fi passwords and associated Bluetooth devices.
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The fastest way to turn off TTY without data loss - use ADB-commands or call resets via engineering menu if a graphical interface is available.
Alternatives to Teletype in Modern Conditions
Teletype technology is becoming a thing of the past, giving way to more advanced solutions. Xiaomi, Poco and Redmi smartphone owners have built-in accessibility features that work much more efficiently, such as Live Caption, which can recognize speech in any application and display it on the screen in real time.
Video calls, where people can use sign language, and instant text messaging services are also widely used. Operators are rolling out IP-Relay services that allow a proxy operator to translate voice into and back without the need for special codes and modes. Current availability standards for Android 13 and 14 completely cover the needs that TTY once closed.
So leaving teletype mode on just in case doesn't make sense. It's just a potential source of communication problems. If you or your loved ones need special communication tools, you'd better set up modern tools in Settings → Special Features, where you'll find Sound Improver, Monor Audio and other useful features.
- 📱 Live Caption for Translating Speech into Text in Real Time.
- 👁️ Increased interface and gesture management for the visually impaired.
- 🔊 Monomode of sound for users with hearing impairment in one ear.
- 🗣️ Voice control and speech synthesis for people with limited motor skills.