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.
Other operational amplifiers in the series, such as the MC34072, MC34074, MC35071, MC35072,...
This circuit is from an old RCA MOSFET manual from the 70s. The circuit can be implemented with...