On HoloLens Device I say "Hey View, scan ", but no reaction. On the same HoloLens Device i say "Hey, Cortana" and I have reaction from device. What can I do for activate voice command from view on Hololens? (I use Vuforia Studio 8.3.2 and last version on Vuforia View)
I found this old post.
Did you check in the HoloLens setting privacy if the microphone permission is allowed for the Vuforia View app?
If your microphone permission is enabled as per Roland's suggestion, make sure you leave a pause between saying "Hey View" and saying "Scan". When you say "Hey View", just wait until the HoloLens generates a short acknowledgement tone, then say "Scan". You may get a response from the HoloLens asking "Did you say Scan?" to which you can answer "Yes".
Funnily enough, try using a slightly American accent also (no kidding!) as this can help!!
I used to have real problems with the HoloLens recognising my Australian accent and it would not pick up "Hey View" unless I used an American access like @bwhelan mentioned. It's gotten better with updates to View and the HoloLens OS, but it's still not 100%.
Note that in addition to "Hey View" you can also say "Hey ThingWorx". It's not in the documentation any more as it's a legacy from when it was called ThingWorx View. I found I could get this to work much better than "Hey View". Hopefully this won't get removed a I still prefer to use it to putting on my bad American accent.
Also, if you want to get back to Scan mode, you can just use the swipe down gesture.