Wireless chargers use an electromagnetic field to charge devices without a direct connection. An induction coil in the charger creates the alternating electromagnetic field, and when this field acts on a similar coil inside the electronic device, it creates current and charges the battery. Most chargers have an extremely short range and require the electronic device to be placed directly on the charging pad to function.
Wireless chargers only work with devices designed to be charged wirelessly, since the process requires a pair of matched induction coils. Simply placing a conventional electronic device on a charging pad has no effect. In some cases, a charging sleeve or adapter may be available that contains the induction coil and a direct connection to the device's charging port.
Wireless charging can be more convenient than traditional direct connection methods, but it is more inefficient due to the energy wasted by the electromagnetic field. These chargers also produce more waste heat than traditional power adapters.
One of the earliest consumer devices to use wireless charging is the electric toothbrush. Braun Oral-B electric toothbrushes have used this technology since the 1990s, since an open electrical port or contact could be dangerous in the moist and humid environment of the bathroom.