You may meet with this kind of problem that when you activate Siri with “Hey Siri”, there is no response. If you have the same problem, just follow the two methods below.
Only the following devices support “Hey Siri” without being connected to a power source: iPhone SE, iPhone 6s, iPhone 6s Plus, iPhone 7, iPhone 7 Plus, iPhone 8, iPhone 8 Plus, iPhone X, iPad Pro (9.7inches or 12.9 inches).
* Turn off Low Power Mode
If you have Low Power Mode turned on, then Hey Siri will not work because it’s a power hog and would be unproductive to the cause of saving power. So you’re suggested to turn off Low Power Mode.
Head to Settings app -> Battery -> switch off Low Power Mode.
* Turn on Listen for “Hey Siri”
Go to Settings app -> Siri & Search -> switch on Listen for” Hey Siri” -> Continue, then complete the following five steps.
* Turn on Voice Feedback
Go to Settings app -> Siri & Search -> Voice Feedback -> Select Always.