The sensors of this liquid alarm are formed by two pieces of wire with the ends peeled off. The relay depends on the supply voltage that can be between 3 and 12 V. The transistors can also be the BC548.
It is a simple blinker that simulates the action of an alarm when installed on the dashboard of a...
The circuit is from a 1978 publication and the transistor may be the BC558. The transformer is...
This simple unregulated circuit was found in a Radio Electronics from June 1964. Note that the...