That Fateful Day

That Fateful Day

Statitrol engineers were working on a device to control static in darkrooms when they discovered the principle that would ultimately make low-cost home smoke detectors practical. Two important factors contributed to the discovery. Advances in nuclear chemistry would allow for a small amount of radioactive material to be used safely, and the industrial progress developing solid state electronics made it possible to engineer low-power circuits that could be battery operated. Adapting circuits to use CMOS semiconductors greatly contributed to reducing power consumption.

Developing an electronic circuit that could use simple 1.5v AA batteries made it relatively inexpensive for single family homes across the country to install smoke detectors. With the addition of a battery voltage monitoring circuit the smoke detector was capable of alerting the homeowner to change the batteries. Adding a led into the circuitry gave the homeowner a way to see the smoke detector was working.

After the accidental discovery, the smoke detection business had its start. The first device to emerge was a new hard-wired commercial system designed and patented by Blackwell using dual ionization chambers and energy-saving inverted triode technology, which he had also invented several years earlier. [Note 1]

Blackwell and Statitrol's staff engineer, Paul Staby, developed and patented self-monitoring circuitry that would cause an audible chirp as a warning when the battery strength deteriorated. [Note 2]

The first unit developed and marketed was named the “SmokeGard 700”. Though it was developed in 1968, the SmokeGard 700 did not receive its Underwriter Laboratory approval until 1973, due to a lack of tests available for this new technology; 1975 marks the beginning of mass production of smoke detection units by Statitrol.

Blackwell and Staby secured the patent on the battery powered home smoke detector on December 11 , 1973 (US Patent Office #3,778,800). [Note 3]

1. Blackwell, Lyman L., "Aerosol Detection Device," United States Patent 4093886A, July 6, 1976.

2. Blackwell, Lyman L. & Staby, Paul A., "Self-Monitoring Battery Operated Circuit," United States Patent 3778800, April 9, 1971.

3. Lucht, David A., “The Most Important Fire Protection Breakthrough in the 20th Century” SFPE, April 24, 2012.

4. Craig Beyler, David Lucht , Margaret McNamee , Peter Johnson and Chris Dubay, "The affordable home smoke alarm, Lyman Blackwell- 2015 DiNenno Prize winner" Fire Science Reviews