Systems, methods and apparatus for wireless charging are disclosed. A charging device has a plurality of charging cells provided on a charging surface, a charging circuit and a controller. The controller may be configured to cause the charging circuit to provide a charging current to a resonant circuit when a receiving device is placed on the charging surface, detect a change or rate of change in voltage or current level associated with the resonant circuit, provide a measurement slot by terminating the charging current for a period of time, and determine that the receiving device has been removed from the charging surface by performing a passive or digital ping procedure during the measurement slot.