It kind of depends on how you define fitness tracker and what features you want on your device. Heart-rate monitors, as well as those that estimate caloric burn, have been around for a longer time (i.e. Polar). Tools using other methods besides heart rate, such as galvanic skin response, have been around commercially since Bodybugg (about 2008). Fitbit came out around 2009.
Some of the newer devices are trying to do both – Polar carries both types of products as does Garmin.