A manufacturer of smart home sensors with an open api for their devices?

Question

Do it yourself

Started studying xbee/zigbee technology as a smart home (home automation) communication protocol.
I found a lot of examples of how to communicate between your sensors based on this technology, but nothing similar for ready-made sensors from a large company. Maximum attempts by enthusiasts to change the bit in the team and hope for the result. I will be glad if my conclusion will be refuted and I will be poked with my nose in the tutorial to interact with the sensor, even for Wulian.
Question: Is there a major manufacturer of smart home sensors (like Samsung, Philips, Xiaomi) that has an open api for their devices? or at least hacked by craftsmen and available for use?

Answer 1

Fibaro (z-wave)
You can see the API level here: https://developer.fibaro.com/
In practice, it turns out to manage devices through the REST API. True, not without the participation of the controller. But it works pretty well.

Answer 2

What sensors are needed?
Check out the sensors: BMP 085/180, 1-wire DS18B20, DHT 11/21/22, LM75, INA219, DS1621, BH1750, AM2321, BME280, SHT21/SI7021, SHT1x, MAX6675, PZEM-004T, CO2 MH-
Z1x can connect to esp8266
firmware homws-smart (WiFi-IoT)