Hi Pluggy1976,
Welcome to the Apple Community.
Re: Devices that support 'Hey Siri'
Seems iPhone 7 does support "Hey Siri" without being plugged into power.
From Apple Support's article: https://support.apple.com/en-us/HT209014
Have you checked if Siri is supported in your country or region ?
iOS and iPadOS Feature Availability
https://www.apple.com/au/ios/feature-availability/#siri
Models that support on-device processing of Siri requests
- iPhone XR
- iPhone XS
- iPhone XS Max
- iPhone 11
- iPhone 11 Pro
- iPhone 11 Pro Max
- iPhone SE (2nd generation)
- iPhone 12 mini
- iPhone 12
- iPhone 12 Pro
- iPhone 12 Pro Max
- iPhone 13 mini
- iPhone 13
- iPhone 13 Pro
- iPhone 13 Pro Max
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Re: tried resetting all of its settings
Wondering if you have turned on "Always Listen for "Hey Siri" "..
Eg: Did you try turning it off, and then turn on again.
Or
You might want to try getting more familiar with Siri, from other Apple support articles.
Seems Siri can learn from you, as you learn to use Siri..
Eg
What can I ask Siri?
https://support.apple.com/en-au/siri
To check out more about using Siri on iPhone iOS 15
iPhone User Guide:
(NB: Click on Table of Contents at the top of the page that opens from the link, to see Siri > topics:)
https://support.apple.com/en-au/guide/iphone/welcome/ios:
All the best :-)