The first rotatable semiautomatic bug was introduced in 1924 and was called the Lytle Triplex. Manufactured by the Precision Thermometer and Instrument Company of Philadelphia, Pennsylvania, it sits on a relatively small base and has an oddly shaped damper. This was a neat small bug with a black or nickeled base .
Copper is on the outside of the spring, and expands more than the steel on the inside.
As the temperature goes up, the spring elongates and the copper bends the spring downward toward the contact point. When the temperature hits 130 degrees Fahrenheit, contact is made and the alarm bell rings. In the example above, touch your mouse to the mercury in the thermometer. Slowly raise the temperature until it is above 130 degrees. As the temperature rises, the bimetallic strip slowly elongates and bends downward toward the contact.