Seeking your assistance:

[themadhippy]

[Kim Christensen]

So lets just imagine for a second that the person above you is "following" you...
What possible purpose could this serve? Seems like a waste of time for the person above.

[SiliconWizard]

There are so many sc*d-up people out there that I wouldn't necessarily be hugely surprised if some were doing just that. Neighbors "spying" on others are a thing, and someone pretty deranged and living in an apartment building trying to spy on people just above or below isn't something that I would find unbelievable.

Technically speaking, thermal cameras would probably do the job. Or mmWave radar(s).

As a corollary of the quote posted earlier, just because you're *not* paranoid doesn't mean they aren't after you either.

[Halcyon]

@dramacydal1 I disagree. Whilst there are a lot of "opinions" out there, you don't have to be a mental health professional to know a thing or two about mental health. For example, I was a police officer for over 14 years and I've dealt with my fair share of mental health patients, hospitals and received countless hours of training.

Likewise, people who might have friends or family members who suffer from a form of mental illness have pretty good insight into these conditions and know a lot more than average Joe in the street.

Take all advice with a grain of salt, but allow everyone the opportunity to have their say. On this forum, we operate under the laws and morales of Australia where, with a few exceptions, anything goes. You don't have to like (or even read) what has been posted.

[Kim Christensen]

Technically speaking, thermal cameras would probably do the job. Or mmWave radar(s).

Yes, but how boring. Just some blobs moving around. I don't know, but if I was going to stalk someone, I'd find other ways like planting audio bugs, cameras, etc within their unit. Or finding some way to hack their computer, baby monitor, door cam, etc... Or even a tiny camera on a stick/thread that could be raised/lowered from a balcony/window to peer into the unit above/below.
If I was really psycho, I'd be drilling small holes to put cameras and microphones through the floor or ceiling. But thermal/mmWave images? Nah.