Pagers
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There used to be systems following different standards.
One of these standards is called POCSAG and there are some information about it at https://en.wikipedia.org/wiki/Radio-paging_code_No._1. Devices only need a receiver, no transmitter, so it is possible to make devices that will not disclose one's location.
The standard allows wide-area coverage, but it depends on every deployment.
As far as I am aware, these messages cannot be confidential and there is no protection against fake messages.