Many users of Xiaomi and Redmi smartphones, accidentally looking into the advanced settings of the phone book, find there a mysterious item called Teletype or TTY. A natural question arises: what is hidden behind this term, is it not a hidden wiretapping function or, conversely, a critical system component that cannot be touched? In fact, this is an outdated, but still supported access technology for people with hearing or speech impairments.
In modern smartphones, including current models Redmi Note i Xiaomi Mi, this function is disabled by default, since the vast majority of subscribers communicate voice. However, the presence of this switch in the menu often causes concern among device owners who are afraid that accidentally activating the mode will disrupt communication or lead to charges. Let's take a look at how this technology works in the MIUI and HyperOS ecosystem, and whether the average user should pay attention to it at all.
Understanding the principle of operation TTY mode will help you not only calm down, but also correctly configure the device if such a need arises for your loved ones with special needs. In this article, we will take a detailed look at the history of the issue, the technical nuances of implementation on the Android platform and give clear instructions on how to manage this function on your device.
Historical background and principle of operation of the technology
Teletype technology, also known as Teletypewriter, was developed long before the advent of smartphones and even personal computers. Initially, these were electromechanical printing machines that allowed text messages to be transmitted over telephone lines. For people with hearing impairments, this became the only way to fully communicate at a distance, allowing them to print text, which was converted into sound signals, transmitted to the interlocutor and printed again on his machine.
With the development of digital communications, the physical teletype machine became a thing of the past, but the data transmission standard remained. In the era of mobile phones, the function TTY was integrated directly into the device software. On smartphones Redmi and other Android gadgets, this function emulates the operation of old equipment, converting voice into text and vice versa directly during a telephone conversation.
The essence of the process is the modulation of sound signals. When you turn on TTY mode, your phone encodes the text you type into specific audio tones that are sent to the telephone network. The person you're talking to, who also has compatible mode or a special app enabled, hears these tones, and their device transcribes them back into text. This requires a stable voice communication channel, since data is transmitted exactly as sound.
⚠️ Attention: The use of TTY mode in modern networks may be unstable due to the peculiarities of voice coding in 4G networks (VoLTE). If you plan to use this function for important conversations, make sure that your operator supports the transmission of text data through the voice channel in your region.
TTY operating modes in the Redmi settings
In the Android operating system installed on devices Xiaomi and Redmi, there are several options for operating the teletype function. These are found in the Accessibility settings menu or in the advanced options of the Phone app. The choice of a specific mode depends on what kind of impairments the user has and how he plans to conduct a dialogue.
The first and most common option is TTY Full (Full teletype). In this mode, the device operates exclusively in text mode: you cannot speak with your voice, and the other person cannot hear your voice. All information exchange occurs only through typing, which is transmitted by sound signals. This mode is suitable for situations where both participants in the conversation are using TTY-enabled phones or special terminals.
The second option is called TTY HCO (Hearing Carry Over). This mode is designed for people who can speak with their voice but have difficulty hearing. When activated HCO you pronounce your phrases in a normal voice, and the interlocutor’s answer comes to you in the form of text on the screen. This allows the user to fully participate in the dialogue without experiencing the discomfort of not being able to hear the interlocutor.
- 🗣️ TTY VCO (Voice Carry Over) - a mode for those who hear well, but cannot speak. You hear the voice of the interlocutor, and type your answers in text, which is converted into sound signals for the subscriber at the other end of the line.
- 🔇 TTY Off (Off) - the standard state of the smartphone. Voice communication works in normal mode, the functions of converting text into sound and back are disabled to save resources and prevent conflicts with codecs.
- ⚙️ Software TTY — on new versions of Android, the function can work programmatically without the need to connect external adapters, which simplifies setup on devices Redmi.
Switching between these modes is carried out through the settings menu. It is important to understand that activating any mode except Offchanges the logic of the microphone and speaker during a call. If you accidentally turn on one of the modes, a normal voice call may be interrupted or accompanied by strange audio interference as the phone tries to modulate your voice into text signals.
How to find and change TTY settings on Xiaomi
The MIUI shell interface and the new HyperOS may differ in different versions, so the path to the coveted setting may vary. Most often, manufacturers hide this function deep in the menu so that ordinary users do not accidentally change the parameters. To access the settings, you will need to go to the Phone application, which is a standard dialer.
Once the application is open, click on the three dots in the upper right corner of the screen to bring up the drop-down menu and select Settings. In the list that opens, look for the section Advanced or Advanced settings. This is where the item Accounts and synchronization or the item itself Teletype (TTY)is usually hidden. In some firmware, the path may lie through the general system settings: Settings → Accessibility → Hearing → TTY.
If you do not find this item in the indicated places, your software version or firmware region may have hidden this option, as it is considered outdated. In this case, you can try using the engineering menu or searching through the settings by entering the query “TTY”. However, for most users, it is enough to simply make sure that the switch is in the position Off.
☑️ Checking communication settings
After changing the mode, the phone may require a reboot to apply the new communication settings. This is normal system behavior, as the configuration of the radio module is changing. Do not be alarmed if, after turning on the mode, the sound in the speakers disappears during a test call - this means that the function is working correctly and is waiting for text input.
The influence of the teletype mode on the quality of communication and the battery
Activation of the function TTY has a direct impact on the operation of the smartphone radio module. Since data transmission is carried out through the voice channel using specific modulation, this may reduce the quality of normal voice communications if the mode is enabled incorrectly. Noise reduction and voice coding algorithms (codecs), such as AMR-WB or EVScan conflict with TTY signals, causing distortion or connection dropouts.
In addition, constantly processing the audio stream to convert text to audio and vice versa creates additional load on the device's processor. Although modern chips can easily cope with this task, in combination with other background processes this can lead to a slightly faster battery drain during long calls. The difference will not be critical, but in standby mode with an active TTY, energy consumption may be higher than usual. Redmi And Xiaomi cope with this task with ease, in combination with other background processes this can lead to a slightly faster battery drain during long calls. The difference will not be critical, but in standby mode with an active TTY, power consumption may be higher than usual.
| Parameter | Normal mode | TTY Full mode | TCO/HCO mode |
|---|---|---|---|
| Use microphone | Continuous (voice) | Only for signals | Continuous (voice) |
| Sound output | Voice of the interlocutor | Text signals | Voice + Tones |
| CPU load | Low | Medium | Medium |
| VoLTE compatible | Full | Limited | Depends on the operator |
If you notice that the phone gets very hot during calls, check if the TTY mode or other special features are accidentally activated in the settings menu.
It is also worth considering that when TTY is turned on, some functions, such as voice dialing or activating the voice assistant Google Assistant during a call may not work correctly or be completely unavailable. The system prioritizes the text data transmission channel, blocking unnecessary audio inputs.
Modern alternatives and relevance of the function
In 2026-2026, the classic teletype is considered an obsolete technology. The development of broadband mobile data and instant messengers has offered much more convenient and high-quality ways of communication for people with disabilities. Applications like Telegram, WhatsApp and Viber allow you to text instantly, send voice messages and make video calls with subtitles in real time.
Modern smartphones Xiaomi and Redmi equipped with advanced accessibility features that replace TTY. For example, the Live subtitles (Live Caption) function automatically recognizes the interlocutor’s speech and displays it as text on the screen in real time, even if the video or call does not have built-in subtitles. This works faster and more accurately than the archaic method of modulating sounds.
⚠️ Attention: The interface and availability of accessibility features may vary depending on the MIUI/HyperOS version and region. If you do not find the features described, check the official user manual for your specific model in the help menu.
Another modern alternative is a call relay service, available in many countries. A human operator or artificial intelligence acts as an intermediary: he hears the voice of one subscriber and types the text for another, and vice versa. This eliminates the need to configure complex technical parameters on the phone itself and provides higher quality communications.
Why is TTY still in the menu?
Manufacturers are required to leave this function in the firmware according to legal requirements in many countries (for example, the FCC in the USA) to ensure communication accessibility for all categories of citizens, even if the technology is outdated.
Problems and solutions
Sometimes users are faced with a situation where the TTY function “sticks” or turns on by itself after a system update. This can lead to the fact that when making outgoing calls you do not hear dial tone or the interlocutor complains about strange sounds instead of your voice. In such cases, the first thing you need to do is perform a complete reset of the phone application without deleting contacts and call history.
To do this, go to Settings → Applications → All applications → Phone. Press the button Clear and select Reset settings (not “Delete data” if you want to save your call history, although in some versions of Android these concepts are combined). After that, restart your smartphone and check whether the TTY switch has returned to the position Off.
If the problem persists, the conflict may arise at the level of the operator’s network settings. Try temporarily disabling the 4G/LTE network and switching to 3G or 2G in the menu Settings → SIM cards and mobile networks → Network type. Test the call. If in 2G/3G mode the teletype works correctly or turns off, then the problem is the compatibility of the TTY mode with your operator's VoLTE networks.
- 🔄 Software update: Check for system updates in the menu
About the phone. Often, bugs with access settings are fixed in security patches. - 📞 Resetting network settings: As a last resort, you can reset Wi-Fi, mobile data and Bluetooth settings. This will delete saved Wi-Fi passwords, but will correct radio module errors.
- 🛠️ Engineering menu: Advanced users can enter a code
##4636##in the dialer, where you can check the phone's status in detail, but be careful when changing parameters without knowledge.
If you are not a user with hearing or speech impairments, the best solution is to completely disable the TTY function to avoid conflicts with modern communication codecs.
Frequently asked questions (FAQ)
Will there be an additional charge for use teletype?
No, activating the TTY mode in the phone settings does not entail additional charges from the manufacturer of the smartphone or operating system. However, the tariff for the call itself depends on your mobile operator. Typically, these calls are charged as regular voice calls, but some older tariff plans may have nuances, so it is better to check with your telecom provider for information.
Can a TTY be used to send SMS?
No, TTY technology is designed solely for transmitting real-time data during a voice call. To send text messages at any time, you should use the standard Messages application (SMS/MMS) or Internet instant messengers. TTY does not run in the background without an active connection.
Why do I hear intermittent beeps when TTY is turned on?
This is normal behavior for idle mode in some protocol implementations. Sound signals indicate that the communication channel is established and ready to receive text data. If these sounds are heard during a normal call, it means that the TTY mode is turned on incorrectly and needs to be disabled in the settings.
Does TTY work via instant messengers (Viber, WhatsApp)?
No, the TTY function built into the Android phone application only works through the classic cellular network (GSM/3G/4G voice). Messengers use Internet channels and their own data transfer protocols, so the teletype system settings do not affect them. To communicate in instant messengers, use their built-in chat functions.
Do you need special equipment to operate TTY on Redmi?
Modern smartphones Redmi i Xiaomi use software TTY, which does not require connecting external devices via an audio jack or USB. All necessary encoding and decoding functions are built into the operating system. You only need a phone with the function enabled and a SIM card with an active voice tariff.