Note from alanocu: Why would anyone have a limit so high ($4000). Not a good idea.
The trap is made up of XRAY film, which is the preferred material by thieves; Simply because of the black color which is similar in appearance to the slot on the card reader.
The trap is then inserted into the ATM slot. Care is taken not to insert the entire film into the slot, the ends are folded and contain glue strips for better adhesion to the inner and outer surface of the slots.
Once the ends are firmly glued and fixed to the slot, it is almost impossible to detect by unsuspecting clients.