What is used to conceal the various mechanisms on the hoistway side of the door?

The correct answer is sight guards. Sight guards are specifically designed to conceal and protect the various mechanisms located on the hoistway side of the door. They help maintain safety and aesthetic integrity by covering components that could pose hazards or disrupt the visual appearance of the elevator entrance.

While other options like "blind covers," "covers," and "panels" could refer to general coverings, they do not specifically address the purpose and function necessary for protecting the mechanisms involved in elevator door operations. Sight guards play a critical role in ensuring that the mechanisms remain unobtrusive and that the elevator system operates smoothly without exposure to external elements or interference. Hence, sight guards are integral to both the safety and functionality of elevator installations.