In tmac's 2017 Teachable Moments article "Let's Fix Replay," suggestion number one to fix MLB's communication problem was "Give the Crew Chief a microphone." Japan's Nippon Professional Baseball Organization has long provided microphones for its umpires to explain complex rulings.
Later that year, MLB began seriously discussing umpire microphones, but ultimately decided against the plan at the time. In 2020, with contract negotiations and a new CBA fresh in the mind of MLB and its umpires, baseball was finally set to embrace the technology, but that plan fell apart when COVID upended the 2020 regular season, as did our aspirations for hearing Joe West ramble on how games are taking too long.
With baseball looking to enter 2022 without pandemic-related restrictions experienced in 2020 and 2021, microphones look to finally be nearing implementation.
Procedure: Following initiation or request of the Manager's Challenge or Crew Chief Review, the Crew Chief (wearing a microphone) shall proceed toward a foul line and address the spectator area and press box regarding the team challenging (if applicable), and the specificity of their challenge (what is being challenged), and the original call. After a review decision has been made, the Crew Chief shall again speak via microphone and communicate the outcome of the review, including whether the call has been confirmed, overturned, or stands, and what the result of the review will be (e.g., the runner is out and the inning is over...Team A loses its challenge).