Owners of Xiaomi and Redmi smartphones often encounter a mysterious setting in the call menu or engineering menu, which is called “TTY” or “TTY Mode”. For an ordinary user who simply calls friends or orders a taxi, the appearance of this term can cause confusion and even slight panic: is it a virus, or maybe the phone has gone into some kind of hidden mode?
In fact, teletype (TTY) is an outdated but still supported text communication technology for people with hearing or speech impairments. In the context of modern smartphones based on Android, including popular models Redmi Note and Redmi K, this feature is often disabled or hidden by default, but if accidentally activated it can block the ability to make regular voice calls. Understanding the operating principle of this protocol will help you avoid communication problems and correctly configure the device to suit your needs.
In this article we will look in detail at why this mode is needed, why it can turn on by itself and how to properly deactivate it if you do not need it. We will also look at the technical nuances of the network and the possible side effects of active TTY mode on the quality of voice communication.
Historical background and principle of operation of TTY
Teletype technology dates back long before the advent of smartphones and even personal computers. TTY (Teletypewriter) was originally an electromechanical device, similar to a typewriter, that allowed text messages to be transmitted over telephone lines. In the modern world of mobile communications TTY mode has been adapted so that people with disabilities can communicate on the phone by typing text, which is converted into audio signals and transmitted to the interlocutor.
When you activate this function on your Redmi, the phone begins to use a special audio channel for data transmission. Voice signals are modulated into tone patterns that are understandable to another teletype machine or specialized software on the receiving device. This means that in full compatibility mode, a normal voice conversation becomes impossible, since the speaker and microphone are busy processing text streams.
There are several variations in the operation of this protocol, which determine which of the participants in the conversation can speak and who can only type. Full TTY mode implies that both devices operate in text format. If one of the devices is normal, the connection may be interrupted or one-way. That is why, for most users, activating this option unnecessarily results in the loss of the ability to make standard calls.
⚠️ Attention: Activating TTY mode can significantly reduce the quality of voice communication or completely block outgoing calls if the interlocutor is not using compatible equipment.
It is important to understand that that although the technology seems archaic, it remains the standard of accessibility in many countries. Cellular operators are required to support the transmission of such signals, which explains the presence of appropriate settings in the firmware MIUI and clean Android. However, with the development of video communication technologies and instant messengers, the need for a classic teletype is gradually decreasing.
Basic operating modes of a teletype in Android
In the settings of your smartphone Xiaomi or Redmi you can find several options for enabling this function. Each of them dictates its own rules for the behavior of the device during an incoming or outgoing call. The correct choice of mode is critical if you really plan to use the phone to communicate with a hearing aid center or specialized services.
The first and most common option is TTY Off (Off). In this state, the phone operates normally, transmitting voice only. This is the default setting for 99% of users. The next mode is TTY Full (Full). Here the device can only send and receive text. Voice communication is completely disabled, and you will see an on-screen interface for dialing messages instead of the end call button or speakerphone.
There are also hybrid modes such as TTY HCO (Hearing Carry Over) and TTY VCO (Voice Carry Over). HCO mode allows the user to hear the other person's voice, but respond only with text. This is convenient for people with speech impairments who have good hearing. In contrast, VCO mode allows you to speak by voice but receive responses in text, which is suitable for users with hearing impairments.
- 📞 TTY Off: Standard voice mode, recommended for all normal users.
- ⌨️ TTY Full: Text only, voice disabled, used for full text communication.
- 👂 TTY HCO: Receive voice, send text, for users with speech impairments.
- 🗣️ TTY VCO: Sending voice, receiving text, for users with hearing impairments.
Switching between these modes is carried out through the phone's system menu or using special USSD codes, which may vary depending on the telecom operator and firmware version. MIUI. Incorrect settings may result in you not being able to hear the other party, or they not hearing you, thinking that the connection is lost.
Where to find TTY settings on Redmi and Xiaomi
Finding the TTY mode control menu can be a difficult task, since smartphone manufacturers often hide these settings deep in the system. On devices with a shell MIUI the path to this option may differ depending on the version of Android and the specific model Redmi. In most cases, the setting is located in the standard Phone application.
To get to the desired item, open the calling application and click on the three dots or the settings icon in the corner of the screen. Select Settings, then find Accounts & Sync or Advanced Settings. Sometimes the required switch is hidden in the “Special Features” or “SIM Card Call Settings” subsection. If you do not see an explicit mention of TTY, it may be hidden in the engineering menu.
You can use the engineering menu secret code to access advanced settings. Type command ##4636##on your phone keyboard. After entering the last characters, the menu should open automatically. Select Phone Information. Scroll down the list to the “Setting your preferred network type” section or directly to the “TTY Mode” item.
##4636##In this menu you will see a drop-down list with the available modes. Make sure that this value is selected TTY Offif you do not plan to use special devices for the hearing impaired. The changes are applied instantly, a device reboot is usually not required, but to be on the safe side, you can restart the radio by turning airplane mode on and off.
If the code ##4636## does not work on your Redmi, try entering the code ##865697## —this is an alternative path to the TTY debug menu on some versions of MIUI.
Connection problems when TTY mode is active
The most common reason why users look for information about a TTY is the sudden loss of the ability to make calls. If your Redmi suddenly stops connecting with subscribers, the dial tone goes off, but no one picks up, or you immediately hear the call being dropped, there is a high probability that the mode TTY Fullis activated. In this state, the phone tries to establish a text connection, which regular networks and subscribers do not support.
Another common problem is audio distortion. If configured incorrectly or attempting to operate in hybrid mode (HCO/VCO) with unsupported hardware, users may hear strange noises, squeaks, or static instead of the other person's voice. This occurs because the audio channel is trying to decode text signals as voice.
In addition, the active TTY mode may affect VoLTE (Voice over LTE) operation. Since TTY uses specific signal modulation, it may conflict with voice protocols over a 4G network. As a result, the phone may be forced to switch to outdated 2G or 3G networks to ensure compatibility, which reduces the quality of communication and the speed of the Internet during a call.
| Symptom of the problem | Probable cause | Solution |
|---|---|---|
| Calls do not go through immediately reset | TTY Full mode is active | Switch to TTY Off |
| The other party cannot hear you | HCO/VCO mode without support | Disable TTY or change mode |
| Extraneous noise and squeaking | Signal encoding conflict | Reboot the phone, reset network settings |
| No Internet during a call | Falling in the 2G/3G network due to TTY | Disable TTY, check VoLTE settings |
If you encounter such symptoms, first check the status of the TTY mode. In 90% of cases, the problem is solved by simply switching the toggle switch to the “Off” position. If this does not help, you may need to reset your network settings to factory settings.
☑️ Diagnosing problems with calls
How to disable the teletype through the engineering menu
If the standard settings menu does not provide an explicit switch, using the engineering menu is the most reliable way to control the TTY function on devices Redmi. This method gives direct access to radio module parameters, bypassing user interface restrictions MIUI. However, you need to act here carefully so as not to change other critical network parameters.
After entering the code ##4636## and going to the “Phone Information” section, find the drop-down list that says “Set up your preferred network type” or simply “TTY mode”. By clicking on it, you will see a list of available options. Select item TTY Off. The system may briefly interrupt communication with the network to apply changes; this is normal behavior.
In some cases, especially on global firmware versions, the TTY item may not be in this menu. Then you can try entering a special command through the “Engineering Mode” application (if installed) or use ADB (Android Debug Bridge) from your computer. The command to force shutdown via ADB is as follows:
adb shell settings put global tty_mode 0This command sets the global parameter tty_mode to 0, which corresponds to completely disabling the function. To perform this operation, you will need to enable USB debugging in the developer options and connect your phone to your PC. This is a more complex method, but it guarantees results if the smartphone software interface has blocked access to the settings.
⚠️ Attention: In the engineering menu, do not change parameters whose meaning you do not know (for example, the preferred LTE/CDMA network type), this may lead to a complete loss of connection.
The impact of MIUI updates on the TTY function
The Company Xiaomi regularly updates the software of its devices, and with each major update MIUI the location of the system settings may change. In recent versions of the shell, developers strive to simplify the interface for the end user, so they often hide technical options, such as TTY, from normal access. This is done to prevent accidental activation, which leads to complaints about non-functional calls.
On some new models Redmibased on Android 12 and newer, the TTY menu may be completely removed from the user interface and accessible only through specialized applications for people with disabilities. If you've upgraded your phone and can't find the old switch, it's likely been moved to Accessibility -> Hearing -> TTY Mode.
It's also worth considering that carriers are phasing out support for classic TTY networks in favor of modern solutions like video calling and real-time text messaging (RTT). Due to this, the feature may be permanently removed as obsolete in future software updates. If your phone model no longer displays TTY settings after an update, this may be a sign that the manufacturer is following the global trend of abandoning this standard.
Why did the settings disappear after the update?
Often, after updating MIUI, custom radio module configurations are reset. If the TTY item is missing from the menu, check the "Accessibility" section. If it’s not there either, perhaps your firmware version has completely hidden this function, considering it outdated for your region. Try resetting the Phone app in the Applications section.
TTY alternatives for people with disabilities
Although TTY mode is still present in smartphones, modern technology offers much more convenient and functional alternatives for people with hearing or speech impairments. Smartphones have powerful built-in accessibility tools that make communication more natural and do not require special codecs or network modes. Android have powerful built-in accessibility tools that make communication more natural and do not require special codecs or network modes.
One such alternative is the (Live Transcription) feature. This is an application from Google, pre-installed on many devices Live Transcribe (Live transcription). This is an app from Google that comes pre-installed on many devices. Redmi, which in real time converts the interlocutor's speech into text on the phone screen. You don't need to switch your phone to a special mode - just place the device next to the audio source, and you will see the subtitles of the conversation.
Another modern replacement is technology RTT (Real-Time Text). Unlike a classic TTY, RTT sends text as you type it, without having to press the Send button. The interlocutor sees the letters as soon as you type them. This feature is integrated into the standard Phone application and works on top of regular voice calls, without requiring switching communication channels.
- 📝 Live Transcribe: Instant voice-to-text conversion for the hearing impaired.
- ⚡ RTT (Real-Time Text): Transmitting text in real time during a regular call.
- 📹 Video calls: Using sign language through instant messengers (WhatsApp, Telegram).
The use of these modern tools is preferable, since they do not limit you in choosing a network (they work on both 4G and Wi-Fi) and provide higher quality communication. If you're setting up a phone for an elderly relative or someone with health needs, these are the features you should look for rather than a legacy TTY.
Modern Android accessibility features like Live Transcribe and RTT completely replace the legacy TTY mode, providing better compatibility and ease of use.
Frequently Asked Questions (FAQ)
Why did the teletype mode suddenly turn on on my Redmi?
Most often this happens by accident when resetting the phone, after updating the firmware, or when using operator-specific USSD codes. Sometimes malware or erroneous actions in the engineering menu can activate this function. Check your call settings and make sure that TTY Off mode is selected.
Does TTY mode affect Internet speed?
TTY mode itself does not affect the packet data speed in standby mode. However, during an active call, if the phone switches to TTY compatibility mode, it may be forced to switch to 2G or 3G networks, where the Internet speed is much lower than in 4G/LTE.
Can I use instant messengers with TTY enabled?
Yes, applications like WhatsApp, Telegram or Viber will work fine, since they use an Internet (IP) circuit rather than a cellular network voice circuit, which is modified by TTY mode. Problems can only arise when trying to make a regular phone call.
Do you need to pay the operator for using TTY?
No, activating TTY mode on your phone is free. However, the tariff for the conversation itself depends on your tariff plan. If the conversation is in text mode through the operator's network, it is usually charged as a regular minute of conversation, and not as an SMS.
What to do if the code ##4636## does not open the menu?
On some new versions of MIUI or with certain telecom operators, access to this code may be blocked. In this case, try downloading the “Activity Launcher” application from the Play Market, find the “TTY Mode” activity in it and run the settings directly through it.