Each competitor in a race is provided with a transmitter. At the finishing line, two receiving antennae (10,11) are mounted which, when the finishing line is passed, are responsive to the field of the corresponding transmitter and permit an accurate determination of the moment when the finishing line...http://www.google.com/patents/US4315242?utm_source=gb-gplus-sharePatent US4315242 - Device for determining the moment when competitors in a race are passing the finishing line
