Siri responds "Uh Huh" for no reason.

I would recommend to retrain the Siri activation word by turning it off and back on. I would also suggest to change the Activation word to "Hey Siri" instead of just "Siri". That will reduce false activations with any sound your phone hears that is similar to "Siri".

Re: "Siri responds "Uh Huh" for no reason.

While I'm sleeping! I just had it happen again, unprompted"

Check your iOS version is up-to-date with the latest

What's new in the updates for macOS Tahoe 26 - Apple Support

says: iOS 26.7 is the latest:

"This update introduces new languages for Live Translation in Messages, Concerts in Apple Music, and 8 new emoji, along with other features, bug fixes and security updates for your iPhone"

Reminder: It is always wise to back up your iPhone before updating iOS.

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Re: "Besides turning off Siri entirely, what else can I do to prevent this?"

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In the short term:

• If your iOS version is already up-to-date:

Restarting an iPhone can often restore order if something is not working as expected. How to: Restart your iPhone – Apple Support

• If you wish, you could try turning on "Do Not Disturb" or setting a "focus" for during the night hours. More info: How to turn Do Not Disturb on or off on your iPhone - Apple Support

• Apple supplies an iPhone Support website (info, / support / Contact options etc.) Scroll to the bottom for links to Support (online chat / phone / email etc.) iPhone - Official Apple Support

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For the longer term:

You may want to send feedback to reach those who work on the software behind-the-scenes at Apple. (You could include a link to this discussion if you want.)

Although they will likely not reply, your feedback will be carefully read and logged, and if others are also experiencing a similar issue, there may be an update that addresses it. (The more feedback received, the more likely it will be addressed.)

Web-form for iPhone feedback: Feedback - iPhone - Apple

or

Apple's Feedback Website: Product Feedback - Apple

Thanks, everyone.

I just ran the latest update on my phone and restarted.

I changed Talk to Siri to "Hey Siri" after turning Siri off and on again. Let's see if this changes anything.

It's pretty unnerving to have your phone say "Uh huh" in the middle of the night.

Thanks again.