The common implementations are scheduled check-ins: the operator confirms presence on a timer, and a missed window triggers release of documents, keys, or statements to chosen recipients. Journalists, operators of services under legal pressure, and holders of sensitive archives use the pattern.
The limits are trust and false triggers. Whoever hosts the switch can read whatever it holds unless the payload is encrypted to the recipients, and a missed check-in for ordinary reasons releases it anyway. Warrant canaries apply the same logic in reverse: a statement that stops appearing.