Hey there - glad you liked it
For this one, I just put my phone in the shopping trolley and tried to angle it so I captured me and and reactions. Very hit and miss, but it was my first try. I didn't try to hide it, so many people use shopping lists on their phone that no-one looks twice if you have your phone out.
I'm also going to try having the phone in my back pocket when recording to see if that is easier to capture reactions. Obviously won't be able to see me, but will hopefully work without a trolley and in any situation (i.e. walking along the street)
To get over recording while the phone screen is off (I've got a cover on mine) - you have to install a recording app (I'm trying out Background video recorder and a couple of others). This allows you to record without people knowing the phone is on.
Would welcome tips from anyone else on the best ways to position the phone