Portable thumb units are rectangular shaped handheld electronic wireless devices with fingerprint scanning technology used in 2015 to collect donations and other funds where a person was unable to access a teller. One such charity collector was Terry, representing the Hill Valley Preservation Society, who came up to Marty McFly asking for a $100 donation to save the Hill Valley Courthouse. Portable thumb units were also used by taxicab drivers, such as Fred, the driver of Cab B25 from the Luxor Cab Company.