A Senate panel has said the implementation of a biometric exit tracking system is a priority for national security.The panel this week pressed the Department of Homeland Security for answers over why such as system has been delayed.The implementation of an automated entry and exit system was mandated by Congress in 1996, and a biometric requirement added in 2004.In response, Rebecca Gambler with the Government Accountability Office stressed that challenges confronted the agency in terms of choosing the best biometric modality and collection method.John Wagner, deputy assistant commissioner atCustoms and Border Protection, also explained different scenarios to show the difficulty of tracking passengers in different environments.Wagner noted that the agency also tested out a plan where Customs officers use handheld devices to gather biometric information as people are boarding a plane.DHS officials said they would continue working on three separate pilot programmes to implement a full biometric exit process.One is using facial-recognition software at John F. Kennedy International Airport in New York City. A separate test is being conducted at 10 of the nation's largest airports, where Customs and Border Patrol officers use handheld devices to get the information at departure gates. And a third test is using kiosks at a land border in San Diego where people entering the country have their irises scanned.