Here is a picture of the metal nose and base of an example ADSID that I believe came from the William Howard Intelligence Museum along with some WW2 Japanese radio items.

Not only were these dropped along the trail, these or similar were dropped or installed around large U.S. bases late in the war. In early fall 1972 I was part of a 4.2” (106mm) heavy mortar unit providing flare and fire support for the Long Binh perimeter (biggest supply base in RVN). We had pre-plotted locations of seismic sensors around the base and would sometimes get calls at night by VHF radio or phone of "movement at sensor so and so" and permission to fire. We did so until the voice at the other end announced “sensor destroyed”… We typically did not go outside the wire and investigate (I only did so once in 2 months with this unit).

best,

brian

kn4r