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.
you can get further back than that. If Wikipedia is a reliable source, here is what they have to offer:
“Leonardo da Vinci envisioned a mechanical pedometer as a device with military applications. The modern all-mechanical pedometer was introduced later to the Americans by Thomas Jefferson. Jefferson obtained a unit from France, but it is not known if he modified the design, or introduced it to the US as is. Although this pedometer is widely attributed to Jefferson, proof is difficult to obtain as he never applied for any patents on any of his inventions. In 1780, Abraham-Louis Perrelet created the first pedometer, measuring the steps and distance while walking.
In 1965, a pedometer called a manpo-kei (meaning “10,000 steps meter” õ©çµ¡®Þ¿ê) was marketed in Japan by Y. Hatano. Y. Hatano promoted “manpo-kei pedometers” from 1985, after his research was accepted as proving that 10,000 Steps A Day was the proper balance of caloric intake and activity-based caloric expenditure to maintain a healthy body, and Jiro Kato who is Yamasa Tokei Keiki Co., Ltd., Tokyo Japan founder, Akira and Yasuji Kato’s Father, manufactured pedometers recognized to be accurate, and, named them, “manpo-meter” (later known as “manpo-kei”) as the world first invented device to measure number of steps of walking. “Manpo-kei” is a registered trademark of Yamasa Tokei Keiki Co., Ltd.”