Checking For Bomb Making (Or Bombs) Remotely

I was thinking about the first attempt to bring down the World Trade Center in the early 90s and it was done with a truck bomb.

The I got to thinking about tall buildings like the John Hancock Building in Chicago. Now a large portion of the building is apartments.

So it seems like if you wanted to bring that building down and you were a rich terrorist (or had their backing) you could rent a bunch of apartments in John Hancock Building and gradually over the years, start bringing up bomb making materials and make a bunch of bombs in various locations (apartments). Then leave the building and have them go off.

This is why I am asking, as obviously that is way too easy, so law enforcement or building management must have “ways” to detect such stuff. I know some landlords require an inspection, but every landlord I’ve had usually limits it to once a year, if that.

Could people walk around with sensors and tell if someone is building plastic or metal type bombs or such?

Yes, either via mobile sensors or probably with bomb-sniffing dogs.