I have a NFC app on my phone, read one of those buttons ... they left it unlocked, so I posted a message. Not sure anyone will read it, presumably they just pick up the location ID in an app. I guess someone could just clone the locations and sit in a chair and spoof it.

Library books in my area use NFC, the tags weren't locked on the last book I checked.

Probably not a security problem (ha!?), but you'd think the possibility of vandalism would cause them to be locked.

I've seen buildings where the buttons are 'burried' in a few mm 'deep' the wall, and painted over so that you don't notice them at all, the wall looks really smooth. The guards know where exactly the spots are, you see them waving their devices in a seemingly flat/blank wall, then the beep sounds, and they walk towards their next 'random' spot.

I've often wondered how often NFC is unlocked like that.

Yep, those have been in retail stores forever. In the grocery store I worked in it was specifically for making sure there weren't hazards on the floor (like a broken jar that fell from a shelf) that someone could slip on and break their neck. It was required by their insurance.

Generally anywhere with security patrols, even outside some residential buildings and townhouses in San Francisco.

It is called "iButton"

https://www.amazon.com/dp/B00R3GRBD8/ref=cm_sw_r_cp_apa_glt_...

That’s a temperature sensor.