Is everyone out in net land familiar with Sensormatic?  They are the company
that make the large plastic clips that set off alarms when you exit a
department store.  I used to work for a department store and the is what
we did.

Open up the clip and remove the shiny piece of paper.  It is about an inch
long and about half an inch wide.  This is the "thingy" (that is the technical
word for it) that sets off the alarm.  This "thingy" is easy to insert into
a pen case, lining of a jacket ...

We did this to a co worker and needless to say, he had problems wearing a
particular jacket to work.