A method and mobile transceiver providing container security is described. In accordance with one aspect, there is provided a method of operating a mobile transceiver comprising a processor, memory, wireless transceiver and radiation detector. The method comprises detecting, by the radiation detector, radiation emitted from a radioactive emitter. The radiation detector and the radioactive emitter are arranged such that a substantially constant rate of radiation from the radioactive emitter is detected when one or more doors of the shipping container are closed. When the detected radiation is outside a tolerance of the constant rate, the processor wakes up the processor from a low power mode, and updates an asset tracking log stored in the memory by adding a record representing a door open event.