The invention relates to radiofrequency transponder circuits, and in particular to such transponder circuits having a unique identifier. Embodiments disclosed include a radiofrequency transponder circuit (100) comprising an antenna module (101), a control circuit (103) and a memory (104), the transponder circuit (100) being configured to respond to a read command received via the antenna module (101) by the control circuit (103) reading and transmitting an identifier stored in the memory (104) via the antenna module (101), wherein the control circuit (103) is configured to perform an integrity check on data stored in the memory (104) upon being powered up by a reader field a first time via the antenna module (101) and to not perform the integrity check for a predetermined time period upon being powered up by a reader field subsequent times via the antenna module (101).
