'locked' mode for handing your device to someone else

[vivlim]

has this ever happened to you?
you're looking at posts on the internet, and you see something cool and decide to show someone else by handing them your phone. but when you hand your phone over, oops! while the phone moved between your hands, one of you accidentally bumped a button, or link, or accidentally scrolled the page, and now you need to find the thing again

what if pillbug had a menu item you could click that would lock the view to a page & prevent navigating away until you unlocked it

probably out of scope: requiring a pin to unlock. i'm not envisioning this as access control, just mitigation for mistakes. though if entering a pin would be useful, i'd consider it