I don't know how to do this but phone can on it's own, caused some concern as emergency services were called by relative who thought I had crashed motorcycle!
If the phone was face-in against your leg I could see how there were "ghost touches" to the point that it did it. If you press the power button as though you're going to just look at notifications on the lock screen, there's an "Emergency" spot on many screens (It may be on the PIN screen), once that is tapped it sounds like your phone has a way to call your ICE contact.
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