Products often need periodic recertification, also known as surveillance. This requirement is typically identified within the certification scheme that the product is certified to. Certification bodies may require product suppliers to perform some sort of surveillance activity, such as pulling sample products from the marketplace for testing, in order to maintain their "listed" or "certified" status. Other examples of Surveillance activities include surprise audits of the manufacturing plant, supervision of the manufacturing and/or testing process, or a simple paperwork submittal from the supplier to the product certifier to ensure that the certified product has not changed. Other causes for recertification may include complaints issued against the product's functionality, which would require removal from the marketplace, and expiration of the original certification. These lists of examples are by no means all inclusive.