A very useful device that, as often technology does, could lead to some twisted uses. The article mentions the possibility to attach something similar to kid's clothes. I already can imagine how many jealous husbands will try to stash one of those things in the wife's bag or car (laugh)
They already have tracking systems in cars and trucks. To make these tracking systems small enough for a human or a pet is not that far fetched. I have seen commercials where a lady has lost her kids and pulls out a tracking device to find him. Science fiction is not very far away.