Aquarium heater ON sensor with thermostat - galvanic isolation 230V

Hi. I have a thermostatic (aquarium) water heater. The heater turns itself on and off depending on the ambient temperature. I need some kind of device that will signal a change in the state of the heater (with a break, short circuit or in some other way), preferably the device would give me galvanic isolation from 230V. I once saw an opto-device of this type, but I can't remember the name or symbol, such a thing would probably be best. Please suggest what I could use or other solutions

Current transformer - complies with requirements

karolark wrote:

Current relay - meets requirements

A simpler application is current relay current relay.

Yes, it was supposed to be a transmitter 😀 - the dictionary corrected it in its own way