More types of electronic devices include answering machines, beepers or pagers, defibrillators, video displays, dongles, doublers, multiplexes, trackballs, artificial pacemakers and monitors. An answering machine is a device that answers the telephone and records messages. A generator is an electronic device used for producing a signal voltage. A digital scanner, or image scanner, is an electronic device that generates a digital representation of an image for data input to a computer. A trackball is an electronic device consisting of a routable ball in housing.