An electronic tag configured to be secured to a body of a person, the electronic tag comprising: an antenna configured to transmit or receive an electromagnetic signal; and an inductive proximity sensor configured to: determine a proximity of a metallic object to the electronic tag, based on electromagnetic coupling between the inductive proximity sensor and the metallic object; and determine, based on the proximity being below a proximity threshold, that a metallic object is attenuating the electromagnetic signal transmitted or received by the antenna; wherein the inductive proximity sensor periodically determines the proximity of the metallic object to the electronic tag; characterised by: a counter configured to have a value that is changed towards a blocked threshold in response to a proximity determination being below the proximity threshold and changed towards an unblocked threshold in response to a proximity determination being above the proximity threshold, and a computer-readable storage medium configured to store a blocked state, wherein the blocked state is set to blocked in response to the value of the counter reaching the blocked threshold and the blocked state is set to unblocked in response to the value of the counter reaching the unblocked threshold. an antenna configured to transmit or receive an electromagnetic signal; and an inductive proximity sensor configured to: determine a proximity of a metallic object to the electronic tag, based on electromagnetic coupling between the inductive proximity sensor and the metallic object; and determine, based on the proximity being below a proximity threshold, that a metallic object is attenuating the electromagnetic signal transmitted or received by the antenna; wherein the inductive proximity sensor periodically determines the proximity of the metallic object to the electronic tag; determine a proximity of a metallic object to the electronic tag, based on electromagnetic coupling between the inductive proximity sensor and the metallic object; and determine, based on the proximity being below a proximity threshold, that a metallic object is attenuating the electromagnetic signal transmitted or received by the antenna; wherein the inductive proximity sensor periodically determines the proximity of the metallic object to the electronic tag; characterised by: a counter configured to have a value that is changed towards a blocked threshold in response to a proximity determination being below the proximity threshold and changed towards an unblocked threshold in response to a proximity determination being above the proximity threshold, and a computer-readable storage medium configured to store a blocked state, wherein the blocked state is set to blocked in response to the value of the counter reaching the blocked threshold and the blocked state is set to unblocked in response to the value of the counter reaching the unblocked threshold. a counter configured to have a value that is changed towards a blocked threshold in response to a proximity determination being below the proximity threshold and changed towards an unblocked threshold in response to a proximity determination being above the proximity threshold, and a computer-readable storage medium configured to store a blocked state, wherein the blocked state is set to blocked in response to the value of the counter reaching the blocked threshold and the blocked state is set to unblocked in response to the value of the counter reaching the unblocked threshold.