People who sit on trains and tubes texting - you need to know, those conversations on your phone aren't private.
Most good-natured people don't pry - but if they want to, they can see what you're writing over your shoulder.
You're not hiding it as well as you think you are.
Thankfully, software is being made to combat this.
A project will be presented at the Neural Information Processing Systems conference in Long Beach, California, on 6 December that will give over-the-shoulder spies something to think about.
Google researchers Hee Jung Ryu and Florian Schroff are to show off an electronic screen protector.
The Google Pixel phone will use its front-facing camera and eye-detecting AI to catch people looking at the screen.
A YouTube demo showed the software interrupt a messaging app to display a camera view, identifying the peeping perpetrator.
The researchers claim the software can work in variable lighting and recognise a person's eyeline in two milliseconds.
It takes 47 milliseconds for face recognition (per face) and 115 milliseconds per frame for face detection, on average.
How long until similar technology is incorporated into advertising?