check in feature iphone 15

Yesterday I noticed a strange yellow square on one of my messages. Had never seen it before. Said something about checking in. I tried to get rid of it but nothing worked. Later that evening in a symphony concert my cell phone alarm went off in spite of the fact that I had silenced everything. Embarassing!! Later I research the term "check in" and discovered a hidden feature of iPhone 15 called Check In. It's not easily found and activated, and so I'm at a loss to know what I did to start it. It's still not clear how to deactivate it, and worse, its alarm overrides notifications. Has anyone run into this issue? Clearly it's something Apple needs to address.