Bingo. The better ones will only accept scantags if you scan the "enter config mode" within 30 seconds after power-on, for instance. Or yes, a hidden button on the underside of the checklane.
That's rare though, and sometimes the installer disables it for convenience while they're debugging the system and never re-enables it. So the vast majority of scanners in the wild will happily accept an enter-config-mode at any time.
That's rare though, and sometimes the installer disables it for convenience while they're debugging the system and never re-enables it. So the vast majority of scanners in the wild will happily accept an enter-config-mode at any time.