Brake light came on on my 2003 BMW X5. Instrument

there is a sensor on the brake pads on bmws that check for noise and when the sensor hears noise it is telling the car that the wear indicators on the brakes are hitting and causing noise because the brake pads(lining) is low,means check your brakes the pads are low and if you dont check them soon you will have no pads left and my grind the pads metal to metal against the rotors,so all it is saying is you may need new brakes because they are worn out
hope that helps,,,