To get around the absence of a physical home button, the "iPhone 8" may let people trigger Siri by holding down the sleep/wake button when they’re not using "Hey Siri."
AppleInsider – Frontpage News
Apple Day – Apple, iPod, iPad, iPhone, iTouch, iMac, iBook
Apple Day – Apple, iPod, iPad, iPhone, iTouch, iMac, iBook