We found this circuit in the 1957 Raytheon transistor application manual. The transistor can be a BC558 and the common 6 V relay, just by using this voltage in the supply.
This circuit is from a 90s Popular Electronics. The transistors are of general use and the buzzer...
This conventional 4 channel circuit with the 4017 and 555 was found in the November 1991 Radio...
This circuit was found in a 1992 publication. The critical component is the photodiode, but...