Thanks for reaching out to the Apple Support Communities! It sounds like you are having an issue with Siri activating on its own and I am happy to help out! Based on what you are describing, there are a couple of things I would suggest testing. First, check out this article About the buttons and switches on your iPhone, iPad, or iPod touch to be sure there is not an issue with any on your device. Specifically:
What to do if a button or switch isn't working
- Restart your device. If you can't restart your device, try to force restart it.
- Remove any protective films and cases that might block the button or switch.
- Check for debris or dirt around the button or switch, and clean with a soft cloth.
If you need help with Touch ID, learn what to do.
If the button or switch still isn't working, is damaged, or works intermittently, you might need to set up service for your device. Contact Apple Support, then follow the steps to complete your service request.
Next, check out this article to Get help with Siri on your iPhone, iPad, or iPod touch and turn off the option for “Hey Siri” to see if Siri still comes on.
Let me know the results and have a great day!