Apart from 4th Amendment questions, there is specific statutory protection regarding wiretapping. At the federal level, chapter 119 of Title 18 is relevant. Section 2511 generally prohibits "wiretapping", via the concept of "intercepting", so whether there is a physical wire for transmitting the signal or the the message wafts across the air, it's the same. Subsection 2 lists a vast collection of situations where interception is allowed. If the agent is a party to the communication, or has the permission of one party to the communication, then it (warrantless interception) is legal, as long as the purpose of the interception is not law-breaking.
Subsection (e) allows a US agent "in the normal course of his official duty to conduct electronic surveillance, as defined in section 101 of the Foreign Intelligence Surveillance Act of 1978, as authorized by that Act". Subsection (i) allows interception in circumstances involving a computer trespasser, which does not seem applicable. Overall, a warrant is required for wire-tapping, and the existence of a physical wire is not required.
A potential escape hatch is subsection (g)(i) which says that "It shall not be unlawful under this chapter or chapter 121 of this title for any person to intercept or access an electronic communication made through an electronic communication system that is configured so that such electronic communication is readily accessible to the general public". It turns out that "readily accessible to the general public" is a technical term defined in 18 USC 2510 (16). Certain things make a signal not readily accessible, one being encryption. Many of these don't seem likely to be applicable, but one has potential, in subpart (e) that the communication is
transmitted on frequencies allocated under part 25, subpart D, E, or F
of part 74, or part 94 of the Rules of the Federal Communications
Commission, unless, in the case of a communication transmitted on a
frequency allocated under part 74 that is not exclusively allocated to
broadcast auxiliary services, the communication is a two-way voice
communication by radio
I cannot hunt down a translation into plain English.