Door buzzer or alarm (CB20492E)

This solar powered circuit was found in a 1991 documentation. The transistor is a general purpose NPN.

Programmed Duty Cycle (CIR095E)
The duty cycle of a Schmitt Oscillator can be programmed by R1 and R2 in this circuit. The...
SCR Complete alarm (CB20474E)
This circuit is from a Popular Electronics from 1992. It uses two SCRs and can be triggered by...
Simple Burglar Alarm (CB4802E)
This simple SCR alarm circuit was found in an old Poptronics, but can be easily assembled as all...