It is fairly simple in theory. The device would consist of a small amount of volatile memory which holds a PRNG seed. A PRNG seed is some initial entropy that deterministically influences the output of a pseudo random number generator. The device would also have an RFID tag capable of transmitting, battery powered RFID can transmit significant enough distances. The volatile memory is hooked to a photovoltaic ('light sensing') cell. After making the package, you would put the device in it and then close it up. Then wirelessly activate the device and load a seed to it. Now when the package is opened light will enter it triggering the photovoltaic cell causing the seed to be wiped from the memory. This makes it impossible for LE to analyze the device to reset it to a non-compromised state. When the package arrives at a fake ID box, the recipient could use an RFID wand to scan for a pattern that they could know because they have shared knowledge of the seed. If they detect this signal, then light never hit the photovoltaic cell, if they do not then either there was a malfunction or an interception. Since they know there was an interception, they can just avoid going to the box store, and since the box is obtained with a fake ID it can not be linked back to them. There are more fine details that would need to be worked out, but that is it in a nutshell. it may even be possible to have it broadcast its interception status after some predetermined time delay, through the cellular network and to a burner phone. We have most of the theory figured out, now the trick is to translate that into a step by step list of instructions on how to create these devices with easily obtained materials, and perhaps to program an open source controller for it.