Connect Xiaomi Mijia Bluetooth Hygrothermograph 2 to the phone: full instruction

Hygrothermograph: Xiaomi Mijia Bluetooth Hygrothermograph 2 (LYWSD03MMC) — It's a compact temperature and humidity monitoring device that's become popular among smart home owners, and unlike the first version, it supports Bluetooth 5.0 and can work without a Xiaomi Gateway, directly synchronizing with a smartphone. However, many users have difficulty connecting for the first time: the device is not detected, the Mi Home app is bugged, or the data is updated with a delay.

In this article, we will discuss three official ways of connecting (via Mi Home, Mi Fit, and alternative firmware), look at common errors and their solutions, and give recommendations for optimal sensor placement. Particular attention will be paid to compatibility with iOS and Android — there are nuances that are not written in the standard instructions. If you just unpacked the device and do not know where to start, follow the step-by-step guide below.

1. What is included in the set and technical specifications

Before connecting, check the configuration of your Xiaomi Mijia Hygrothermograph 2. The box should include:

• 📦 The sensor itself (white or black case with display)
• 🔋 Battery CR2032 (It is already installed, but there may be a protective film)
• 📄 Short instructions in Chinese/English
• 🧲 Magnetic stand (in some versions)

If something's not there, it's a good idea to go to the vendor, and now we're going to look at the key characteristics that affect connectivity and performance.

The important point: if your device has a marking LYWSD02, This is the first version of the sensor that requires connection via the Xiaomi Gateway. LYWSD03MMC Direct Bluetooth connection.

2. Preparation of the device for connection

Before connecting the sensor to the phone, follow several mandatory steps:

1. Remove the protective film from the battery. There's a little hatch on the back of the sensor -- put a nail on it or a flat screwdriver -- and there's a thin film under the battery that blocks the contact.
2. Activate the sensor. Once the battery is installed, the Bluetooth symbol should appear on the display (🔵) If the screen is empty, press and hold the button on the back for 5 seconds.
3. Check the compatibility of the smartphone. The device works with Android 5.0+ iOS 10.0+, But there are limitations on the iPhone (more on this below).

If the sensor does not turn on after the battery has been installed:

• ⚡ Check the polarity of the battery (plus should be on top).
• 🔄 Try rebooting the sensor: Remove the battery for 10 seconds, then insert back.
• 📱 Make sure your phone has Bluetooth enabled and location permission enabled (required for Android!).

Warning for iOS users: Due to Apple’s limitations, the Xiaomi Mijia Hygrothermograph 2 sensor can only connect via the Mi Home app in Mainland China. When choosing other regions (e.g. Russia), the device will not appear in the list of available. This is not a mistake – this is how Apple’s policies for Bluetooth devices work.

3. Connect via the Mi Home app (main method)

This is the most reliable method that works on most devices.

1. Download and install Mi Home. 📥 Android / iOS 🌍 When you first start, select the region of China (Mainland China) – this is critical for the correct operation of the sensor!

Register or log in to your account.

If you already have a Xiaomi account (for example, for a smartphone), use it. If not, create a new one through an email or phone number.

Add the device.

Press. + → Add the device → Sensors. → Temperature and humidity → Xiaomi Mijia Bluetooth Temperature and Humidity Monitor 2.

Follow the Connection Wizard.

The app will suggest turning on Bluetooth and allowing geolocation access, and then you start looking for the device, and when the sensor appears on the list, click on it.

Set up the update parameters.

By default, the data is updated every 10 minutes, you can change the interval by 1, 5 or 30 minutes (the less often, the longer the battery lasts).

If the sensor is not located:

• 🔄 Reset the sensor (remove the battery for 10 seconds).
• 📱 Restart Bluetooth on your phone.
• 🌐 Check that the region of China is selected in Mi Home.
• 🚫 Make sure the sensor is not connected to another device (e.g., a tablet).

Attention! ⚠️ Once connected, the sensor can display incorrect data in the first 10 to 15 minutes. That's OK -- it needs time to calibrate. Don't reconnect the device during this period.

4. Alternative ways of connecting

If Mi Home isn’t suitable (for example, due to iOS restrictions) or you want advanced features, consider these options:

Method 1: Mi Fit App (for iOS)

This is a solution for iPhone owners who can’t connect via Mi Home:

1. Download Mi Fit (App Store)
2. Select China region when you first launch.
3. Go to Profile. → Add the device → Temperature and humidity sensor.
4. Follow the instructions on the screen (similar to Mi Home).

Limitation: Mi Fit does not allow you to change the data update interval – it is fixed (10 minutes).

Method 2: Custom firmware (for advanced users)

If you are not satisfied with standard software, you can flash the sensor with alternative firmware (for example, PVVX or ATC_MiThermometer). It gives:

• 📊 Exporting data to Home Assistant, InfluxDB.
• ⚡ Reduce the refresh interval to 1 minute.
• 🔧 Advanced calibration settings.

Warning! ⚠️ Third-party firmware is insecure and can lead to unstable work. If you are not sure about your skills, it is better to use a standard solution.

💡

If the sensor is connected but the data is rarely updated, try placing it closer to the phone (within 5-10 meters), walls and furniture can weaken the Bluetooth signal.

5. Typical errors and their solutions

Even with the right connection, users face problems, and here are the most common ways to fix them:

If the sensor is connected, but after a while disappeared from the list of devices:

1. Check if your Bluetooth settings on your phone are down.
2. Remove the sensor from the Mi Home and reconnect.
3. Update the Mi Home app to the latest version.

Attention! ⚠️ Android 12.+ Some vendors (Samsung, OnePlus) are aggressively optimizing background apps. If the data is no longer updated, add Mi Home to the battery-saving exemption list.

6. Optimal placement of the sensor

The accuracy of the reading depends on the location of the installation.

• 🌡️ Height: Place at 1-1.5 m from the floor (not on the floor or under the ceiling).
• 🚫 Avoid: direct sunlight, kitchen (steam from stove), bathroom (condensate).
• 📶 Signal: If you use your smartphone to collect data, keep the sensor within a 10m radius.
• 🔋 Battery: in cold rooms (below) +5°C) the battery will run out faster.

Use sealed covers (sold separately) to monitor greenhouses, aquariums or refrigerators, remember that high humidity (over 80%) can damage the electronic components of the sensor.

💡

The ideal location for the sensor is the north wall in living rooms, away from windows and appliances. Avoid areas with sudden temperature changes (for example, near the air conditioner).

7.Integration with a smart home

The Xiaomi Mijia Hygrothermograph 2 sensor can be linked to other smart home devices for automation:

Examples of scenarios:

• 🌬️ Air humidifier: switched on if the humidity is below 40%.
• ❄️ Heater: turns off at temperatures above 24°C.
• 🚰 Watering plants: Start if the soil is dry (an additional sensor is required).

To set up the automation:

1. Open Mi Home and go to Automation → Create → Smart scene.
2. Select a condition (e.g., "Temperature") > 25°C").
3. Add an action (for example, "Enable air conditioning").
4. Save the script and activate it.

If you have a Xiaomi Gateway, the sensor can be used in complex scenarios with other devices (lamps, sockets, motion sensors).

💡

For stable automation, make sure that the phone you’re connected to is always in Bluetooth range (or use the Xiaomi gateway).

FAQ: Frequent questions