Many Xiaomi smartphone owners, exploring hidden menus or engineering settings, stumble upon a mysterious item called “Teletype Mode” or TTY Mode. This option is often puzzling, since its purpose is completely unobvious to the modern user, accustomed to touch screens and voice communication. Most people simply ignore this option, fearing that an accidental change in settings will lead to malfunctions in cellular communication.
TTY is not a virus or a system bug, but an outdated but still supported technology designed to help people with disabilities. In today’s Android reality, this feature is disabled by default, since its activation can block incoming calls or change the format of voice transmission. Understanding how this mode works will allow you to protect your phone from accidental communication failures.
In this article, we will discuss in detail what the acronym Teletypewriter hides, why this mode is built into the firmware MIUI and HyperOS, and whether the user should interfere with these settings at all, and we will look at the technical aspects of the protocol and provide step-by-step instructions for managing this feature.
Historical background and purpose of technology
TTY stands for Teletypewriter, which means teletype. Initially, it was an electric typewriter connected to a telegraph or telephone network that allowed text messages to be transmitted over long distances. In the context of mobile communications, this technology was adapted to make communication accessible to people with hearing or speech impairments who could not fully use a regular voice channel.
When you activate this mode on a Xiaomi smartphone, the device switches to a special modem modem modem, the voice signals are converted into text or tone signals that are transmitted to the interlocutor. If there is also a TTY-enabled device on the other end of the line, it decodes the signal back into text, which allowed deaf people to conduct full-fledged phone conversations long before messengers and video communication.
Modern smartphones emulate physical teletype software. Android, which runs MIUI shells, has software support for various voice protocols, but with the ubiquity of high-speed Internet and applications like Telegram or WhatsApp, the practical need for classic TTY for the average user has almost disappeared.
- 📜 Historically TTY It was used to transmit news and stock quotes before faxing.
- 📞 The main goal of introduction into mobile phones is social adaptation of people with disabilities.
- 📱 In modern smartphones Xiaomi function works as a software emulation of old equipment.
It's important to understand that activating this mode changes the logic of processing the audio stream. The phone stops perceiving the line as purely voice and starts looking for text packets of data. Unless you're a deaf or hard of hearing person using specialized equipment, you won't need this feature.
Principle of operation and available modes
Xiaomi phones typically have four TTY protocol options available in their settings, each telling the phone how to process the incoming and outgoing signal, and understanding the difference between them is critical if you accidentally activate the feature and can’t reach or hear you.
TTY Off mode is standard for 99% of users, in which the phone is in normal voice mode, and activating any other mode puts the device into a specialized mode of operation, which can affect the sound quality or the ability to make calls.
TTY Full is designed for users who can neither speak nor hear, and in this mode, all incoming voice messages are ignored or converted into text (if the other person is using TTY too), and your phone only sends text. Voice communication in the classical sense becomes impossible.
There are also hybrid options: TTY HCO (Hearing Carry Over) allows the user to hear the other person but respond with text, which is convenient for people with speech impairments, while TTY VCO (Voice Carry Over) allows voice to speak but receive textual responses, which helps people with hearing impairments.
| Regime. | Incoming linkage | Outgoing linkage | Who's it meant for? |
|---|---|---|---|
| TTY Off | Voice. | Voice. | All users (standard) |
| TTY Full | Text | Text | Deaf-mute users |
| TTY HCO | Voice. | Text | Speech disorders |
| TTY VCO | Text | Voice. | Hearing impairment |
Switching between these modes is done through a system menu or special codes, and it is worth noting that cellular operators can support transmissions in different ways. TTY-signals, especially in networks 4G and 5G, where voice is transmitted by a batch method (VoLTE).
Where to find TTY settings in the Xiaomi interface
Depending on the version of the Android operating system and the MIUI or HyperOS shell, the location of the teletype settings may differ; in older versions of firmware, this item was often hidden in the developer menu, but in modern builds it was brought to the public to comply with accessibility standards.
To find this setting, you need to go to the basic settings of the device. The path usually looks like this: open Settings, then select Special Features. Inside this section, you need to find a category related to hearing or phone. In some versions of MIUI, the path may look like Settings → Advanced Settings → Special Options → Hearing.
☑️ Checking availability settings
If you can't find "Teletype Mode" on the path, try searching by settings. Click on the magnifying glass at the top of the settings screen and type in "TTY" or "Teletype" and the system will redirect you to the menu if this option is supported by your model and current firmware.
In some cases, especially on global firmware versions for certain regions, this item may be hidden or removed by the manufacturer, since in specific countries the use of firmware is not possible. TTY not regulated or replaced by other Relay services, in such a situation, activation is possible only through the engineering menu or ADB-Teams, but it requires high qualifications.
⚠️ Attention: Change of settings TTY Any mode other than "Off" can cause you to stop hearing audio in the speaker on normal calls.
How to turn on or off the teletype function
If you find that the mode is active and interferes with normal communication, it must be turned off. The deactivation process is simple and does not require root rights. Go to the settings menu as described above, find the Teletype Mode and select the TTY Off value. Changes take effect instantly, rebooting the device is usually not required.
To enable the feature (for example, if you are testing compatibility with hearing-impaired equipment), select one of the modes: Full, HCO or VCO. After selecting, the system can warn you that standard voice calls may not be available or the speaker's behavior will change. Confirm the action.
There is also an alternative way to manage via the codeable engineering menu: Open the Phone app and type ##4636##. From the menu that opens, select Phone Information. There may be a drop-down list for setting up TTY Mode. However, on many modern Xiaomi models, this code may not work or hide these options.
What to do if the settings are reset?
When you change your settings, you're encouraged to make a test call. Notice that a special TTY icon appears in the status bar at the top of the screen. If the icon is on, it means that the mode is active. To return to normal life, this icon must disappear.
The effect of the regime on network and battery operation
Activating the TTY protocol has a direct impact on how the smartphone's radio module works, and as the phone starts processing the audio stream differently, either by converting it to text or waiting for text packets, this can lead to increased power consumption. Although the difference won't be huge, battery discharge can occur a little faster in standby mode.
In addition, enabled TTY can conflict with modern voice technologies such as VoLTE (Voice over LTE) and VoWiFi (Voice over WiFi).In some cases, the phone can forcefully switch to 2G or 3G networks to ensure compatibility with the teletype protocol, which reduces the quality of communication and speed of mobile Internet during a conversation.
- 🔋 Increased battery consumption due to constant signal processing by the modem.
- 📉 Possible decrease in the quality of voice communication and the appearance of interference.
- 📶 Forced switching to older communication standards (2G/3G) in some regions.
Users may also find it impossible to use hands-free or Bluetooth headsets in some TTY modes. The system blocks additional audio channels to avoid conflicts with the stream of teletype data. So if you have lost the sound in your headphones or the headset in your car stopped working, check this setting first.
💡
For stable 4G/LTE performance and minimal battery consumption, always keep TTY mode off unless you use special devices for people with disabilities.
Frequent problems and ways to solve them
One common problem is that teletype mode is spontaneously turned on. Users notice the TTY icon on the screen and can't figure out how it came about. Often this happens after updating the system, resetting settings, or installing some calling apps that have their own accessibility setting priorities.
If the standard shutdown through the menu does not help and setting "gray" (inactive), the problem may lie in the operator profile. Some SIM cards when registering on the network send a command to enable certain services. → SIM-maps and mobile networks → Select a network, disable automatic selection and try to register on another available network, then return the automatic selection.
It's also worth checking installed apps. Third-party calls or conversation recording programs may have their own accessibility settings that override system ones. Removing newly installed telephony-related apps often solves the problem.
⚠️ Attention: If the icon TTY It burns constantly, and you can't turn it off, try resetting your network settings. It won't delete your personal data (photos, contacts), but it will return all network settings to factory values.