Embodiments described herein provide various designs of multi-frequency radio frequency identification (RFID) tags which are compact in size and tamper-proofing. In one aspect, a proposed multi-frequency RFID tag includes both a high frequency (HF) subsystem and an ultra-high frequency (UHF) subsystem. The HF subsystem and the UHF subsystem share a common integrated circuit (IC) chip and a common substrate. The HF subsystem further includes a HF loop antenna coupled to the IC chip. The UHF subsystem further includes a coupling antenna electrically coupled to the IC chip but electrically isolated from the HF loop antenna. The UHF subsystem also includes an UHF antenna having a region for receiving the RFID module. When the RFID module is positioned within the receiving region of the UHF antenna, the UHF antenna is coupled to the IC chip in the RFID module via the coupling antenna, thereby forming the UHF subsystem.