ఆటోమేటిక్‌ ఫైర్‌ అలారంను మొదటగా ఎప్పుడు కనుగొన్నారు?
The first automatic electric fire alarm was patented in 1890 by Francis Robbins Upton, an associate of Thomas Edison. George Andrew Darby patented the first European electrical heat detector in 1902 in Birmingham, England. In the late 1930s Swiss physicist Walter Jaeger tried to invent a sensor for poison gas. He expected that gas entering the sensor would bind to ionized air molecules and thereby alter an electric current in a circuit in the instrument. His device did not meet its purpose: small concentrations of gas had no effect on the sensor's conductivity. Frustrated, Jaeger lit a cigarette and was soon surprised to notice that a meter on the instrument had registered a drop in current. Smoke particles from his cigarette had apparently done what poison gas could not. Jaeger's experiment was one of the advances that paved the way for the modern smoke detector. In 1939 Swiss physicist Ernst Meili devised an ionization chamber device capable of detecting combustible gases in mines. He also invented a cold cathode tube that could amplify the small signal generated by the detection mechanism to a strength sufficient to activate an alarm.
1890