Passive tag including volatile memory

A semi-passive tag which communicates with a Radio Frequency Identification (RFID) reader, the semi-passive tag comprising:

• a sensing unit which senses or measures information about environmental surroundings of the tag;
• a volatile memory;
• a non-volatile memory;
• a power receiving unit which receives an RF signal including operating power of the tag from the RFID reader;
• a power supply unit which supplies power required to operate the tag;
• and
• a control unit which monitors first and second power levels of first power received in the power receiving unit and of second power available from the power supply unit, stores resultant data sensed or measured by the sensing unit in the volatile memory, and moves the data stored in the volatile memory to the non-volatile memory when the first power level falls below a first threshold or the second power level falls below a second threshold different from the first threshold,
• wherein the control unit is further operative to transmit to the RFID reader a signal indicating that insufficient power remains when the power remaining in the power supply unit is insufficient to operate the tag.