For me on my Iphone7 seems like siri won't do anything much without unlocking the phone first. I can get the weather but if want to open the weather page I still have to unlock. I can turn off an alarm or make a new alarm but can't get in the alarm app without password.
I think they have closed all the ways people used to get into your locked phone with Siri a few upgrades ago. I am sure there will be someone somewhere with more time on their hands and nothing to do and will figure out another way of hacking in.