What’s the best thing about having a large open-source community of developers? You get access to affordable, cutting-edge tech.
This is a Xiaomi Mijia Temperature Humidity Sensor. You can usually find these on Aliexpress for around $2-5. The device comes equipped with Bluetooth Low Energy (BLE), which is perfect for maintaining long battery life. A GitHub user (atc1441) has released custom firmware for this device, allowing you to send telemetry data to other devices. When paired with a single ESP-32, this device can do some amazing things. I currently have about 7 of these sensors paired to a single ESP-32 and couldn’t be happier with the results.
You can learn more about this project and follow the guide here.