How to Stop Cops From Using Your Utility Meter to Spy on You (youtube.com)
Smart meters log your daily routine minute by minute detail. Law enforcement can pull this data across the country (US). It paints a pretty detailed picture of what's going on in your home, because every device has a power consumption profile. Your devices use different voltages etc. Not only cops, but also the government is interested in this info.
You should have a battery between the grid and your devices, because then the grid just charges the battery.