You can check the life left in your brake pads by yourself, you only need the tools in your spare tire kit!
Oftentimes, squeaking can be caused by brake dust or you may have something lodged between your brake pad and the rotor (like a small rock).
Click on the video below for a quick tutorial on how to check the life left in your brake pads:
There are other indicators that your brakes may need to be serviced. If you own a front wheel drive car, when you step on the brakes, if you have vibration in your steering wheel, you may have warped rotors. When you replace your rotors, you always need to replace your brake pads, however when you replace your brake pads, you don't always need to replace your rotors.
When you do decide to change your brake pads, you can look for obvious signs that your rotors are warped by looking for uneven wear on the brake pad.
Your brakes are the only thing made to slow you down, so don't neglect them!