We found this circuit in an old Mullard (Philips) documentation on the 555 and 556 integrated circuit (double 555). The relay must be 12 V with contacts that support the horn current.
This circuit with only one transistor was found in Japanese documentation from the 1960s. The...
This circuit was found in documentation from Analog Devices from the 90s. The circuit uses...
This sensor circuit from a 1967 Ferranti documentation uses components from the era. The circuit...