We found this circuit in an article in Electronics Now magazine from November 1997. The circuit uses two transistors to measure the temperature difference between them when one receives the wind.
An advanced motor control software plug-in for Microchip’s MPLAB® X Integrated Development...
This relay without lock uses a general-purpose transistor. The relay is according to the supply....
This signal follower is from a 1970's documentation. So it uses the traditional configuration at the time...