Sony WI-1000XM2 Help Manual page 111

Note
Siri cannot be activated when you say "Hey Siri" even when the iPhone's "Hey Siri" setting is on.
When using the voice assist function, your voice will be heard from the headset through the headset's microphone (Sidetone
function). In this case, ambient sounds or the sounds of the headset operation may be heard through the headset, but this is not
a malfunction.
Siri may not be activated depending on specifications of the smartphone or application version.
Siri does not work when connected to a device not compatible with the voice assist function.
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