Squeaking brakes can be very dangerous if they are not diagnosed and fixed in a short frame of time. The squeaking you hear from the brakes could be due to a number of things but it will commonly be due to age. There are easy ways to stop this noise and get an extra lease of life out of your car brakes.
The first and most obvious way to troubleshoot squeaking brakes is to look at them. Quite often brakes will squeal because a small object or build up of dirt is causing the brakes to grind. Use a car jack to raise each corner of the car into the air at a time. Support car with jack-stands for safety. This will allow you enough room to slide beneath the car and take a look at the inside as well as the outside of the wheel. Look to see if the brake discs are obstructed or whether there may be some debris beneath the car's body causing the brakes to tighten.
Remove each wheel of your vehicle in turn. This will allow you to get a good look at the brake pads and rotors. These parts of the brake may be covered in dust or dirt. This will cause friction when the brakes grind and it will produce a high pitched squeaking noise. The simplest solution is to use a brake cleaner spray and clean these parts of the brake. This will clean them and reduce the amount of friction substantially. Levering the tire off of each wheel will also help you to inspect brake pads more closely.
A reason for squeaking brakes can be the caliper bolts, which may be too tight. You can access these by leaving the car raised and by using a set of general use wrenches. Make adjustments to the bolts if they are too tight and tighten them up if they are too loose. Squeaking can occur at these bolts because they will either not be secured correctly or covered in dirt. Clean them with the same spray. These bolts will be easy to notice because they are the two largest bolts near the brake mechanism on a wheel.
Sometimes squeaking brakes will make a noise because the parts of the brake are too aged. Small grooves can appear on the rotor and brake pads. When air blasts through these parts when a car slows down, these grooves create a circle, which will produce a whistling sound. The way to stop this is to replace the rotor or brake pads yourself or take the car to a garage to have this done.
You have to keep your brake fluid reservoir filled up. Check if the level of fluid is between the maximum and minimum lines. Top it up if it is below the minimum line. The brake pads have a wear squealer built into them to indicate worn pads. If the squealer is making noise, then it is time to replace pads.