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Tamper-proof transparent security plate

  • US 4,228,425 A
  • Filed: 02/06/1978
  • Issued: 10/14/1980
  • Est. Priority Date: 02/06/1978
  • Status: Expired due to Term
First Claim
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1. A tamper-proof transparent security plate comprising:

  • a break-resistant, normally transparent plate structure which becomes opaque upon forceful penetration, said plate structure comprising a pair of break-resistant glass plates laminated to one another by a thin layer of polyvinyl-butyral plastic which becomes opaque upon breakage;

    a transparent alarm plate containing a plurality of frangible electrically connected conductive wires extending across an area to be protected, said alarm plate is laminated to said plate structure and comprises a single sheet of glass containing said wires embedded within said sheet; and

    a variable voltage source connected to said wires for varying the current passing through said wires to provide said security plate with an optional heating, de-icing, or defogging capability.

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