The Fitbit Surge was released in 2015 and is identifiable by model number FB501BKL. This is a smartwatch that is capable of monitoring your heart rate, pace, elevation, and distance.
It is common for the bands on the Fitbit Surge to fall off completely or crack/wear out. The band is not replaceable as it is permanently attached to the Surge, therefore the whole unit has to be replaced. You can contact Fitbit support here and see what their options are.