The numbers around domestic violence are staggering:

http://ncadv.org/learn-more/statistics

It's also a notorious blind spot for law enforcement – even when restraining orders are issued, they're nearly unenforceable, and once the aggressor is in your house you're a sitting duck.

Ambient audio-UI devices could be the biggest technological break ever in monitoring for the presence and emotional state of the subject of a restraining order. It's not obvious like a security camera or alarm system, and opt-in to a monitoring app would be invisible.