An Apple Siri mystery has been solved by an audio engineer — spectrogram reveals how Apple stopped voice assistant setting off millions of iPhones and HomePods during its WWDC 2026 event

• Apple avoids setting off your iPhone when its execs say “Hey Siri” at events
• One enterprising engineer decided to find out why
• By analyzing the keynote’s audio, they solved an intriguing mystery

Siri has just been given the brain transplant it's needed for years, but it's always been good at detecting the words "Hey Siri" — so much so that accidental summonings have been a common problem. But an audio engineer has just explained how Apple cleverly avoided Siri popping up on your phone during its recent WWDC 2026 keynote.

As revealed by Techexplain on Substack, it all comes down to the audio frequencies embedded in Apple’s keynote video. Once Apple’s audio engineers made a few subtle tweaks, the company’s presenters could say “Hey Siri” as much as they liked without risking millions of phones going off around the world.

To find out what was going on, Techexplain downloaded the audio and video from the WWDC event. They fed that into a spectrogram analyzer, which is an app that can visualize audio frequencies as colored graphs and bands. When the WWDC video was examined, it revealed that a few frequency bands in the 3kHz to 6kHz range had been removed from the audio.

And this is the key to the video not invoking Siri. Without those four frequency bands, the Siri assistant lurking on your device did not hear the phrase “Hey Siri” — even though Apple’s presenters said it repeatedly throughout the show.

Wait, how exactly does this work?

Apple’s solution might sound odd. After all, doesn’t Siri listen out for the trigger words being spoken? If those words were present in Apple’s video, shouldn’t Siri have been activated?

Well, not quite. Your iPhone contains an “always-on processor” chip whose job is to constantly sample background audio, which is then fed into a neural network. The audio is converted into a spectrogram and the neural network analyzes it to look for a specific frequency pattern — in this case, the sibilant sound that occurs when you say “Siri.” And yep, you guessed it, those sibilant sounds mostly exist in the 3kHz to 6kHz range.

In other words, what Siri is actually listening out for is a frequency rather than the words being spoken. It means that if Apple’s engineers remove the 3kHz to 6kHz bands from the WWDC keynote, Siri won’t “hear” its name being spoken — even if that’s exactly what the presenters are doing.

It’s a clever trick that helps ensure Apple’s presenters can speak naturally without the need to avoid saying “Siri.” At the same time, it avoids setting off millions of iPhones and annoying their owners when “Hey Siri” is uttered. It’s an ingenious solution that solves a thorny problem in a satisfyingly elegant way — and we wouldn’t expect anything less from Apple.