That makes too much sense in most circumstances.

However, when dealing with a dense collection of stacked non-metallic items, the HHMD wands may not beep on a small metal object (like a bullet perhaps) concealed inside/in between a sizeable collection of certain non-metallic materials, like say my earlier reference to a stack of magazines of certain paper stock. I don't know about concealment of a small metallic object inside a rather dense collection of rubber bands from real reports being as effective vis-a-vis the HHMD wands, but even if the HHMD doesn't work having the OP cut open the rubber ball probably was a more common sense approach than arresting them on imagined drug use.