Wireless personal information carrier having logic for connecting a battery only during data transfers

An information carrier in a preferred embodiment is worn like a dog-tag and carries data such as medical information. The tag operates wirelessly, communicating with a nearby reader which interrogates the tag with a selected combination of RF signal frequencies. Extremely long term battery usage is achieved by connecting the battery in the tag only when the proper combination of RF signals, each at least at a minimum threshold power level, is received at the tag to produce a trigger voltage in activation logic to close a solid state switch. After a sequence of communications between the reader and the tag is then completed to transfer selected data from the memory, the battery is again disconnected to preserve battery energy for very long periods of time. The battery may be slowly recharged by ambient energy using a scavenging antenna array.