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LYWSD03MMC
https://pvvx.github.io/ATC_MiThermometer/TelinkMiFlasher.html
The LYWSD03MMC is a Bluetooth temperature and humidity sensor manufactured by Xiaomi. According to the search results:
It can be converted from Bluetooth to Zigbee by flashing a custom firmware onto the device.[1][2] This allows it to integrate into smart home systems like Home Assistant and ESPHome that support Zigbee devices.
It has an LCD screen to display temperature, humidity and battery level.[3]
Custom firmware has been developed to run on the LYWSD03MMC that converts it to a Zigbee device rather than Bluetooth, allowing it to connect to platforms like Zigbee2MQTT, ESPHome and Home Assistant.[4][5]
Guides exist online on how to flash this custom Zigbee firmware onto the LYWSD03MMC using a USB to serial converter to convert it from Bluetooth to Zigbee.[6][7]
It is an inexpensive $4 temperature and humidity sensor that can be made compatible with various smart home platforms by flashing open source custom firmware onto it.[8]
[1] Converting Xiaomi LYWSD03MMC Temperature sensor … - Reddit [2] atc1441/ATC_MiThermometer [3] Xiaomi Mijia BLE Sensors - ESPHome [4] devbis/z03mmc [5] Xiaomi Temperature & Humidity Sensor Home Assistant Integration … [6] Convert Xiaomi LYWSD03MMC BLE Sensor to Zigbee [7] Home Asssistant Xiaomi Mijia LYWSD03MMC Temperature and … [8] 4$ Xiaomi thermometer custom firmware LYWSD03MMC … - YouTube