I am writing a mobile app for a bluetooth device which I did not create / invent. To do this, I received specs from someone else on how the device communicates over Bluetooth; it's a non-standard, not open protocol (How this person obtained the specs of the non-standard protocol is unknown).
Is it illegal to write an app, market and sell it, that can control this bluetooth device?
Since the company that created the device also has an app, but it's insufficient and users are complaining about it.
For the sake of argument, we could call the Bluetooth device a remote controllable color changing light. It uses a non-standard protocol. The company is based in China; but has offices in some other countries as well. I am located in South Africa.