Rearview mirrors are glued snug to your windshield, but that doesn't mean they don't occasionally fall off.

They can come off for a number of reasons, including a crash, accidental impact like bumping with your head, jerking it too hard while adjusting, as well as sun exposure and constant vibration that causes the adhesive to wear down.

"Most of the modern windshields [are designed to] prevent sun exposure [to the adhesive]," said Mike Delaney, owner of Patriot Auto Glass in Ashburn, Va. "But age and heat can still play a role."

If your car's mirror does fall off, it's important to have it replaced as soon as possible, as your car's rear visibility will be significantly reduced.

Fortunately, you can reinstall a rearview mirror on your own in just a few short steps. It's simple enough to do, and DIY kits are available at any auto-parts store. Many auto glass technicians also will reinstall them for a fee.

Follow these steps if you're reattaching your car's rearview mirror:

Tools and materials needed: DIY rearview mirror reattachment kit, window cleaner, razor blade, hair dryer (optional).

1. Remove the mounting button from the rearview mirror. The mounting button is what attaches to your windshield. It's typically removed from the mirror assembly by either sliding it off or screwing it off from the mirror's arm.

2. Apply heat to the windshield.

Brian Daniels, owner of Glen Allen Glass & Mirror in Ashland, Va., said it's important to make sure the windshield is warm before the glue is activated. A cold windshield can cause condensation, which can prevent the glue from sticking to the glass. "If there's moisture and you try and apply the glue to the surface, it won't stick, period," he said. Daniels uses a hair dryer to warm up the windshield.

3. Clean the windshield and remove old adhesive.

Before you install the mirror, make sure the surface of the glass is squeaky clean. If there's any remaining glue on the windshield or the mounting button, try to remove it with a razor blade. Once the glue is gone, use a glass cleaner or cleaning alcohol to clean the inside of your windshield and the backside of the bracket that will stick to the windshield. Daniels said to make sure your fingers don't touch the windshield to avoid any oils from getting on the glass.

4. Make your mark.

If you have an older vehicle, use tape on the outside of your windshield to show exactly where you want the bracket to go on the inside. Delaney said many newer vehicles come with a black band on the outside that shows where the bracket should go.

5. Apply an activator.

After that, use an activator spray on both surfaces - the inside of your windshield where the bracket will go and on the backside of the bracket itself. Let the activator dry for a few minutes.

6. Place glue on the mounting button.

Daniels says you should place the glue on the bracket, sometimes called the button, but not on the windshield. Firmly push the button onto the windshield and apply pressure for 60 seconds. Make sure that you applied the adhesive to the right side of the bracket.

7. Attach the mirror to the bracket.

Delaney recommends waiting five minutes for the bracket to fully adhere to the windshield before connecting the mirror to the bracket. Attach the mirror to the mounting bracket per the manufacturer's instructions.