From artist Bjørn Karmann, Alias is perhaps the first decent attempt to permanently intercept the way in which voice assistants, such as Alexa/Echo and the Google Assistants, work.
As we all know, such devices are handy to have around the home but are a trade off for user privacy. These devices are essentially passive snoopers: recording machines which send one's data back to an anonymous centre elsewhere in the world. Alias works by, literally, plugging into the device.
Karmann's thinking is based on real organic parasites:
We looked at how cordyceps fungus and viruses can appropriate and control insects to fulfill their own agendas and were inspired to create our own parasite for smart home systems.
The device is a Raspberry Pi within a 3D-printed shell, that literally clips onto the device. The job of the Pi is to intercept the assistant by broadcasting a quiet signal to it, thus prevent it listening to its environment. A user-defined "wake word" can stop the broadcast and allow active communication with the assistant again.
Because it operates independently of the device, it is also possible to generate new commands for the Alias which cannot be achieved with the assistant alone. This offers, for example, the opportunity to shout all sorts of childish, sweary words at the assistant and let the Alias decode it into a "permissable" command.
All of the code is available on GitHub, and Bjørn has published a how-to guide on building it. More here.