Law enforcement officials in most U.S. states have quietly deployed controversial handheld scanners as part of an effort to interdict suspicious funds held on prepaid cards and other magnetic-stripe products. The Electronic Recovery and Access to Data (ERAD) scanners permit users to verify the card numbers and legal holders of debit and credit cards seized from a suspect, and to ascertain and temporarily freeze balances stored on seized prepaid cards after the suspect consents to a search or investigators establish probable cause. The readers also give law enforcement agents a tool to determine whether criminals are reprogramming and using the...