We found this circuit in a 1968 General Electric publication. The circuit uses an SCR of the time, but any modern equivalent can be used. The relay must have contacts that support the horn current.
The circuit whose characteristics are given in the graph uses two transconductance operational amplifiers...
This circuit was found in the Radio Electronics magazine in an article about emitter-coupled...
This circuit was obtained from an 80s factory manual. The integrated circuits used are uncommon...