A warrant is required only as long as "voice assistant" technology "is not in general public use"[1]. Kyllo v United States created a bright-line[3] test that removes the warrant requirement to see "details of a private home that would previously have been unknowable without physical intrusion"[2] when use of the technology is normalized.
Note that this removes the warrant requirement in general, even if you personally don't own an Alexa/etc. The test is if the public expects audio in the home might be recorded and sent to a 3rd party. If the answer is "yes", then the police can use their own hardware to do the recording.
Note that this removes the warrant requirement in general, even if you personally don't own an Alexa/etc. The test is if the public expects audio in the home might be recorded and sent to a 3rd party. If the answer is "yes", then the police can use their own hardware to do the recording.
[1] http://caselaw.findlaw.com/us-supreme-court/533/27.html
[2] Ibid.
[3] https://en.wikipedia.org/wiki/Bright-line_rule