https://www.theverge.com/circuitbreaker/2017/9/3/16249026/iphone-8-siri-power-button-rumor

Since the upcoming, premium iPhone won’t include a physical home button, Apple has reportedly come up with at least one new way of triggering Siri with an actual button on the device: it will use the sleep/wake/power button. Developer Guilherme Rambo, who has already unearthed details about the “iPhone 8” and other coming Apple products like the HomePod and a 4K Apple TV, claims to have found a “gesture to invoke Siri by holding the lock button.” 9to5Mac and MacRumors both reported on the discovery.

Apple’s preferred way for users to interact with Siri will almost certainly remain voice and the “Hey Siri” callphrase. But having a reliable, consistent way of pulling up the iPhone’s digital assistant without speaking to your phone is important — both as a backup and for consumers who are simply more familiar with holding a button to access Siri.