The clear plastic thermoformed blister is most often combined with a printed card which has a heat-seal coating so the plastic blister can adhere to the card.  Sometimes in place of the printed card, foil, plastic or laminated materials are bonded to the pre-formed blister.  If this style of package were tampered with, it would be obvious thus the blister package is a very popular style when a product must remain secure for the end user.  These are commonly used for pharmaceutical products, but many, many general consumer goods use this economical and effective packaging style.