At first glance I was worried about the privacy implications of OpTag but I'm reassured by the stated motivation
Oh well that sounds just fine.
Up to 5% of aircraft departure delays are caused by late passengers or late bags at the gate, and the impact of this in missed slots and subsequent costs will increase as the number of flights increases. The OpTag system will enable the immediate location of checked-in passengers who are either missing or late, and thus reduce passenger-induced delays and speed up aircraft turn around.
Oh wait, perhaps there is an alternative. Why not forget the privacy-invasive necklaces and just pull back from the gate at the designated time. If Billy-Jim loses track of time in the 'Some Name Here Brewing Company', bad luck for him. He can catch the next flight to the Shriner's convention.