Anti- Shoplifting RF Sensor

This was asked back in 2002 with no good answer. I wondered if there were newer members now that would know how to make those RF sensors that you see at Target next to the door to prevent "Shrink". Schematics would be nice. I would also like to know the parts required. I also know that not many would have schematics but I'm sure someone has schematics. Anyway, That's really it.

It is a simple tuned circuit.
It is a conductively printed inductor with a series or parallel capacitance.

A tuned parallel LC circuit produces a high voltage swing that can be detected.
A tuned series LC circuit produces a high current swing that can be detected.