[ianmf]

These devices are funded by government/school systems. When you receive them, you have to sign a TOS or User agreement, where highly likely contains a verbage similar to "This device is subject to monitoring". This is the magic statement; it notifies you that they could be watching, and you are aware and agree to the search.

The consent banner is typically mandatory on all government IT systems. Here is the one for the DOD: https://dso.dla.mil/

[waste_monk]

I vaguely recall some (possibly apocryphal) story about someone who beat criminal charges back in the early days of computing by arguing that since the equipment they hacked in to did not have such a banner, it was clearly intended to be for public use.