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 alternating flasher was found in a 1980s documentation. The transistors may be equivalent such...
The purpose of this circuit is to measure the resistance of an antenna at the resonant frequency....
When light fails to focus on the sensor, a common photo-transistor, the relay closes its contacts....