Which phones are getting "Hey Cortana"

The Lumia Denim firmware update brings Microsoft's Cortana voice assistant.

But some Lumias will also get the "Hey Cortana" feature.

At the moment it's only for two Lumia models - the 1520 and the 930.

It uses passive listening technology to know when you say "Hey Cortana" when the phone is on any screen and activates the assistant ready to answer your questions instead of the long hold of the Search button.

Microsoft says it hopes to push it out to other devices soon.