If the back cover of your Timex watch has come off by accident or if you have had to replace a dead battery, it is important that you replace the back cover correctly. If your Timex watch is designed to be waterproof, improper installation of the back cover could allow water to easily enter the watch. Some models have the device responsible for sound attached to the back cover as well.
Inspect the back of you watch. Pay special attention to any rubber gasket that may be in place. This rubber gasket helps with waterproofing, and can easily be damaged if it is not aligned properly. The gasket should fit snugly around the circumference of the watch case. Misaligned gaskets can cause the back cover to not snap as it should.
Place the watch face down on a soft cloth to protect the watch face. Look at the back cover of the watch for an indentation. If there is an indentation in the cover, align it with the winder of the watch. If there is no indentation in the cover, place it over the back of the watch.
If there is a small metal disc on the inside of the back cover, this is the sound mechanism. Place the cover so the spring coming up from the watch touches the metal disc.
Press down on the watch cover firmly. Use an even amount of pressure of both sides of the cover until you hear it snap into place. Some Timex watches require a small mechanical press to be closed securely. If you are unable to snap the cover back on with your hands, take the watch to a professional watch repair shop.