How do i know when to change my toyota corolla 2007 brake pads?

I old Ford Focus car make squeaking sounds when i was driving and not using the brakes letting me know to get the pads changed but my corolla made no sounds like that but just today I noticed that my corolla makes a grinding sound when I start coming to a complete stop. This makes me think that the pads are completely worn and the rotators are getting grinded down. I read something saying that toyota uses cheap pads so they don't make sounds when you break where my ford was very loud when I would break letting me know that my pads needed to be replaced. Are my rotators messed up or is something else going on.