when the brakes are low/need replacing are there any indicator lights that light up or is it just the sqeaking noise?

 

There is an indicator light!!!!

 

there would be both. you'd heard the squeak first then you'll see the light. when the ilght comes on i would definitely change it out that weekend to save the sensor. you can damage the sensor with prolonged use, and replacement is not cheap (though there is a trick to disable and never use it again).

 

I had a squeek coming from my front driverside brakes, so i decided to spend $250 on brand new high performance brake pads, pulled all the hubs apart and found all my brakes had heaps of meat left on them, but i replaced them anyway. The squeek is because the bottom lip of my rotor wasnt burred out yet to match the rest so i have to deal with the squeek till it burrs. My brake warning light has still remained on tho, i dont see how the sensor has been damaged due to heaps of meat on old brakes, but could of happened anywhere over the past 23 years lol.

 

My understanding follows - please feel free to correct me if you have better information.
The sensor is a simple switch made from joining two wires. (which form a closed circuit).
But when the pads wear to the point where the sensor "head" contacts the rotor, the contact point is worn through, the circuit is broken and the warning light will turn on.
You will be lucky if you can catch it in time after the warning light goes on, until the sensor is permanently worn through.
[Edit add -> Upon further reflection, I don't think this is possible. Once the warning light goes on, the sensor is permanently ruined.]
Since it costs above $50, it might be well to change the pads before you see the light.

The workaround mentioned above is just to remove the old sensor, then short the two leads together.
This tells the warning light that everything is OK, and you should never see it light again (even if the pads are completely worn out).
Of course, you don't have a sensor any more.