Based on a 555, this 80's American documentation circuit detects the voltage of a battery and can then disconnect the charger. The transistor may be a general purpose type.
This simple oscillator with two general-purpose transistors has its frequency given by capacitor...
This flood or humidity alarm was found in an English publication in 1991. It can still be fitted...
We found this interesting configuration in a 1976 technical documentation. Equivalent diodes can...