{
  "patent_number": "US 1537326",
  "country": "US",
  "title": "How Early Telephone Systems Managed Busy Lines Automatically",
  "original_title": "Make-busy scheme for telephone systems",
  "summary": "A 1925 patent describing a mechanism to automatically signal that a telephone line is occupied, preventing callers from interrupting an active conversation.",
  "what_it_does": "The patent describes a make-busy circuit designed for automatic telephone exchanges. When a specific telephone line is currently in use, this circuit applies a potential—a specific electrical voltage—to the test terminal of that line. This signal effectively marks the line as busy, so that if another caller attempts to connect to it, the automatic switching equipment detects the signal and prevents the connection from being completed.",
  "what_it_does_not_cover": [
    "Does not cover digital or packet-switched communication networks.",
    "Does not cover call-waiting features that allow a second caller to interrupt an active line.",
    "Does not cover software-based line management systems.",
    "Does not cover wireless or cellular telephony."
  ],
  "filed": "1922-08-28",
  "granted": "1925-05-12",
  "expires": null,
  "status": "active",
  "holder": "Automatic Electric Co",
  "holder_url": "https://patentbrief.org/company/automatic-electric-co",
  "inventors": [
    {
      "name": "Bernard D Willis",
      "url": "https://patentbrief.org/inventor/bernard-d-willis"
    }
  ],
  "times_cited": 0,
  "tags": [
    "telecommunications",
    "mechanical"
  ],
  "abstract": null,
  "url": "https://patentbrief.org/patent/us/1537326/insulin-extraction-and-purification",
  "markdown_url": "https://patentbrief.org/patent/us/1537326/insulin-extraction-and-purification/md",
  "google_patents_url": "https://patents.google.com/patent/US1537326",
  "relatedPatents": []
}