That seems like a huge security risk.They actually do have voice recognition but not the home units as they are supposed to be used by anyone that is in the house, unlike your phone. The latest Android phones learns your voice and actually ignore other people's "Ok Google" promps.
I reckon Burger King did more than "hack" the device, they hacked the media. I mean look at how much media cover they getting now, vs an ad that had a limited run for no extra cost.
Burglar: Ok Google, give keys.