The active device would be a low power electronic device that is designed to log any attempt either failed or successful to view or tamper with the contents of a parcel from the time it leaves the sender until the time the intended receiver is deciding whether or not to take delivery of the parcel (they could scan the device from a distance using Bluetooth on there phone to check if there had been any questionable activity).
How would this device fare from a legal standpoint both domestically (either Australia or elsewhere) and when sent internationally?
While not explicitly intended to snoop on postal workers or anyone else specifically it would include the capabilities to listen in on its surroundings in order to perform its primary task, additionally it may log its location for the duration of the journey.
Also obviously it will require a power source - while Lithium ion batteries are restricted I believe that under a certain size there still able to be sent, at least by Australia Post unless I am miss interpreting there website. But I don't know about other countries - are there restrictions on non rechargeable power devices?