Not that easy
These devices have a low power chip that listens continuously for anything resembling "Alexa" or "OK Google". When it hears something that matches it sends a recording to the cloud for speech recognition. Putting proper speech recognition into a low power chip would be difficult.
The strange thing is that early attempts at speech recognition (what you say) turned out to be voice recognition (who is speaking) devices. The down side is that antique tech requires training. Say "Siri recognise my voice" a hundred times and a low power chip probably could (but it would also respond to you saying "OK Google" or "OW! Who spread drawing pins on the floor?"). The problem is to find customers with enough brains to understand the problem, enough patience to actually train the device and sufficient courage/gullibility to let such a device in their home.
Biting the hand that feeds IT
