Alexa et al are also normalizing "always on microphone that sends audio to a remote business over the internet" technology . According to the bright-line rule from Kyllo v United States [1], when a technology is "in general public use"[2], police no longer need a warrant when they use their own devices based on that technology to see the "details of a private home that would previously have been unknowable without ph…
You cited the summary, which may be useful but isn’t legally binding. The actual opinion starts after “Justice Scalia delivered the opinion of the Court.”
Also, Kyllo isn’t relevant to your concerns. A microphone and radio which picks up audio and transmits it is a technology which has been around for more than 60 years. Use of that technology has been addressed by the court in Katz and its predecessors, which collectively found that warrantless use by the police of such tech is often prohibited by the fourth amendment.
A more relevant question is whether the fourth amendment would allow police to access records stored by Amazon in the case of conversations picked up by Alexa devices. Usually, such data is fair game (third-party doctrine), but there are some constitutional restrictions (See e.g., *Carpenter v. U.S., 2018). However, even if there were no restrictions, the question is probably moot because other laws (Wiretap Act, Stored Communications Act) restrict police behavior. Basically everyone believes that these restrictions apply to Alexa recordings.
Recently there was a case in which a police department served Amazon with a subpoena for Alexa recordings from the scene of a suspected murder. I don’t remember the outcome in that case, but that too is irrelevant to concerns about warrantless collecting or searching of Alexa data, because there a warrant was or could have been obtained.