This invention relates to a seal for sealing a freight container. The seal includes, in its in-use configuration, a shaft (18) and heads (20) on opposite ends thereof. It includes also an electronic circuit (40) including a radio frequency identification (RFID) transmitter (42) and sensing means (44, 46) for sensing severance of the shaft (18). Severance of the shaft (18), if sensed by the sensingmeans (44, 46), is detectable by interrogation of the RFID transmitter (42) via a compatible interrogation device. A basic embodiment of the seal comprises parts made mostly of a non-conductive, vulnerable material. Should operational requirements so dictate, additional parts are provided for effectively, in the in-use configuration of the seal, reinforcing the vulnerable parts to yield a tamperresistant seal which still may be interrogated to determine integrity of its shaft. Other embodiments of the seal permit also interrogation to determine the integrity of another part of the seal.