Xiaomi has launched a new smart door lock in China that includes an intercom voice changer, letting you disguise your identity while speaking with someone at the door.
This is closed source, so not that great. But it's still a cool idea.. they should add it to phones.
Source: https://www.notebookcheck.net/Xiaomi-Smart-Door-Lock-2-New-model-with-voice-changer-unveiled.986666.0.html