They can be disconnected from the net

A publicly-funded group of designers, artists and privacy experts from Amsterdam have designed an intelligent home system prototype to "prove it's technically possible to build a privacy respecting smart home while maintaining convenience".

You probably weren't expecting this

Apple's Homekit has a bug which allowed people to not only open your front door remotely, but unlock your garage, switch your smart plugs off and on, and mess around with your thermostat.