A candle warmer is a small electric heating pad. It allows you to enjoy a candle's scent by warming the wax without lighting the wick. They are usually used with jar candles (candles made by pouring wax, gel or another scented substance into a glass pot), which fits into the crock pot-like warmer. Some candle warmers come with an adapter to hold pillar candles as well.
No Flame, But...
Some people use candle warmers to experience the scent of their candles in places where flame is impractical or forbidden. It's true that there is no open flame when a candle warmer is in use, which does mitigate that hazard. However, a candle warmer is an electrical device, and so—as with anything that you have to plug in—it is not totally without risk. The same precautions must be taken with a candle warmer as with any other wired gadget.
Never operate any electrical device without understanding the manufacturer's instructions. Any machine that contains a heating element may overheat, so never leave a candle warmer unattended if it is in use. Turn it off and unplug it when you're not using it. Exercise caution with the power cord; be sure to keep it where it won't be accidentally tugged on or tripped over. Discontinue use immediately if the cord is damaged. If the warmer falls, unplug it before you pick it up. Something may have broken inside, therefore posing a shock risk.
Candle warmers work by heating the candle to release its scent into the air. They use a very low temperature, but there is still a risk from softened or melted wax. Exercise caution if using a candle warmer around children or pets, and check to make sure that the wax has hardened and the jar is cool before removing it from the warmer.
If your candle warmer ever smokes or gives off a burning smell, turn it off and unplug it immediately. It may be that the warming element is overheating, or you may be using a type of candle that has a lower burning point than the warmer was designed to handle. Even if it is working perfectly, don't leave it unattended. Any electrical item may fail or overheat without any warning.
Keep it Dry
As with any electrical device, keep the candle warmer away from all liquids. Even a grounded appliance may cause a nasty shock if you touch it with wet hands, and electricity and water are a real fire hazard. If something does spill on or near your candle warmer, turn off the power before you unplug the warmer. If you can't unplug it right away, then dry your hands completely and unplug the warmer using a wooden tool, such as a broomstick or salad tongs. If those items are unavailable, then unplug the warmer while wearing thick rubber (not plastic) gloves.