Why is Siri continuously being activated without pushing home button?

Today, I was at the gym with my headphones in. IPhone 6S Plus was not glitching for the first 10 minutes, but then it kept activating Siri without me even pushing the home button. Thinking it was being pressed in my pocket, I took it out and set it on a flat surface with no way the home button could be pressed. Needless to say, the issue continued.
Obviously, I became irritated, unplugged my headphones, and set my iPhone behind the front desk. Now at home, my iPhone is not doing it at all.
I m thinking of getting new headphones to see if it was a headphone issue, but that doesn t explain the Siri problem.

Has anyone else experienced this? What fix is there to look into?

I have had the phone sine February 1, so if it continues, I may just replace the phone.

Thank you in advance for any answers.

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