Constitutions normally only protect the content of communications, not the fact that communications occur. This isnt even the traditional metadata debate (inside v outside of an envalope). They dont care who or what you text, just the when and that you did. A mandatory tech that betrays only the time that a text was sent will probably survive legal scrutiny.
4A makes no distinction between content/things and actions. A timeline of my actions is absolutely something I am (should be) secure in.
Furthermore, the idea that privacy means secrecy is too narrow even when we think only about personal information, like the contents of a journal. Suppose I give you my diary and urge you to read it. No one would think you are violating my privacy when you do so. The reason is that privacy is not about the information itself, no matter how personal it may be. Instead, this aspect of privacy – informational privacy – is about my right to control what other see, and in this example I have given you my permission.
Privacy has less to do with the information we conceal from the world than with the close and trusted people that we determine to share our information with.
My Actions, i.e. the act of communicating, is absolutely protected under the original intent of the fourth amendment. Now, that means very little nowadays, but your statement -
"Constitutions normally only protect the content of communications, not the fact that communications occur" - is patently untrue.
