1- You hear a squealing noise
Today, most—but not all—brake pads are manufactured with built-in “wear indicators.” The sole purpose behind these things is to emit that unpleasant screech you just heard. Wear indicators are metal tabs located near the top of typical brake pads. When the pad itself wears down to a dangerous extent, the indicator will scrape against the rotor. This creates a distinctive grating noise which warns the driver that his or her current pads are in danger of eroding away altogether.

2- You hear a clicking noise.
In some cars, the brake pads fit snugly into a special holding device. Other vehicles keep them steady with clips, bolts, or pins. At all rates, the common goal behind these designs is to keep the pads from wobbling around. If they become loosened somehow (perhaps after a part of the surrounding hardware gets damaged), they’ll begin to rattle. What then results is a clicking sound that rings out whenever the brake pedal is pushed or released.

3- Bringing the car to a stop takes more time than it used to.
This problem has a name and that name is “brake fade.” More often than not, it’s the direct result of intentionally applying the brakes over a vast distance without bringing the car to a full stop. By forcing the pads to make contact with the rotors for a long, uninterrupted period, both components will heat up. In the process, their ability to generate needed friction against each other is reduced over time. As a result, you’ll find that your car won’t come to a complete stop as rapidly as it once did.

4- The nose of your car pulls to one side when you brake.
Your vehicle’s brake pads won’t always wear out at the exact same rate. Sometimes, those on one side will get thinner faster than their counterparts on the other side. Should this occur, the car may pull slightly to the left or right once you hit the brakes. Leave the problem unchecked, and you’ll put unnecessary stress on your steering rack (plus your vehicle’s ball joints, steering knuckles, and wheel bearings). Don’t risk it: Have a mechanic investigate the problem immediately.
Note that brake pads might not necessarily be the cause behind this particular symptom. It may also stem from such other issues as uneven tire pressure, a faulty wheel bearing, or malfunctioning brake caliper. With that said, if unevenly-worn pads really are the culprit, two new sets should be installed in one session.

5- The brake pedal vibrates when pressed.
Does the brake pedal violently shake whenever you step on it? Pads might be causing the problem. Brake pads are typically held together with a kind of binding resin. As each pad wears down, this adhesive gets hot and gets smeared across the rotor. Under ideal circumstances, it will form a layer that’s evenly spread over the disc’s surface. But if a pad gets overheated, the resin may not be distributed uniformly. Mechanics call this issue “glazing” and it can cause brake pedals to vibrate.
A pulsating brake pedal isn’t a trustworthy one. If this issue goes unchecked, your ability to brake safely could be compromised. When it comes to brake pad upkeep, stay safe and don’t procrastinate.