The basic switch idea, upper left is two non-corrosive stainless steel bent in upside down "U" to hang over cup or soup bowl edge. A two conductor flexible wire with end connector plug holds the two stainless steel wires by one leg and other leg is hooked over side of vessel at height to fill. As liquid rises, hot or cold, contact is made through liquid and legs of hook to active turned on suitable sound alarm for blind person or who is doing drinks in the dark.
You can determine what you want switched on.
