How to use "boundary" in a sentence

What's more, there was a force field at the city boundary that was impossible to cross: there were alarms there that sensed your wrist chip before you even got close, and then government agents appeared in seconds to arrest you

"Well, I suppose I'm thinking that maybe, just maybe, there is still life in the outside world - and maybe someone from that world has found a way across the city boundary."

He truly didn't believe the fruit came from another world beyond the city boundary - and she couldn't really blame him

I've been trying to send a message for many years, but nothing has crossed the boundary successfully

"Who are they? How did they get it across the boundary?"

If the government finds out that messages are getting through the force field and passing across the city boundary, there could be big trouble."

She's able to cross the boundary."

Then maybe they would help us escape across the boundary."