Abstract: An alarm system includes a sensor/control unit and an antenna unit, each mounted to a support member which may be disposed around an edge of a door of a container or the like, with the antenna unit outside the door and the sensor/control unit inside the door. Clamps are provided to hold the system to the door. The system may thus be removed and transferred to another container as desired. The sensor/control unit contains a radio transmitter, which transmits data via the antenna unit to a remote receiver. The sensor/control unit may also contain an alarm against unauthorized entry or tampering, a tracking system, and/or telemetry sensors to monitor the interior of the container, for example for cargo condition, temperature, or illicit contents, such as contraband or stowaways.