Belts do not randomly squeak. Either the belt is loose and needs to be tightened or one of wheels it turns is going bad and needs replacing. I suggest you fix the actual problem and not the symptom if you don't want to be stranded somewhere.
A squealing serpentine belt is an indication that the belt is pretty close to the end of its useful life. Usually, that is. It could be that one of the accessories that it is driving is dragging too much.
Use hand soap, (be careful) give yourself room for error but run vehichle and rub hand soap on belt it will stop sqeak. Or maybe try to rub on belt before you run it, it takes a steady hand to perform what i mentioned above. Good Luck