The invention relates to a wireless communication device that is coupled to an energy source, such as a battery, capacitor, or solar cell. The wireless communication device is coupled to a slot in the energy source to form a slot antenna for wireless communication. The slot antenna receives communication signals from an interrogation reader or other communication device. The wireless communication device may be attached to a device or container for purposes such as communicating information regarding identification, manufacturing, tracking, and the like. The wireless communication device may also be coupled to the energy source for power.