Mr. Mangerson, who owns a company called Wavsys that builds cell service networks, considered installing an intercom on his roof deck, but he was quoted a price of $2,000. And giving every visitor a mechanical key in advance would have been impractical, if not impossible. Instead, he paid a few hundred dollars for KISI, an access-control system that, like the Schlage lock, allows users to control the lock with a smartphone and distribute “e-keys” to visitors.