The Marshall Project: A Phone Call From Jail? Better Watch What You Say by Ken Armstrong:
A confession, a threat—it’s probably taped. And admissible.
Although people do things against their own interest all the time, even the police can be amazed. Moe Greenberg, a Baltimore County police detective, is the author of Detective’s Notebook, an advice column for fellow investigators. One time he wrote: “Most facilities that record inmate’s calls or visitations play a preliminary recorded message informing the inmate that their call or visitation will be recorded. One would think that this would eliminate any references to criminal acts, actions, knowledge, or involvement. Despite this very clear warning to the inmate, they still talk!”