Out witted

I went shopping today. Into Northampton Town with the remaining family.

I had this brilliant idea that I was going to blip them from this little walkway in one of the little shopping centres.
I made my excuses and said I would catch up with them...
Not once was I able to take a picture of them unaware.

This is the closest I got.

How do people KNOW they are being watched and from what direction?
It beats me.