Since these devices are several years old, the internal lithium-polymer battery may have degraded. If buying used, ask the seller how long a single charge lasts.

If you are looking to purchase one today, here is the best way to go about it:

The Fitbit One still works with the current Fitbit app , but you may need the original USB charging cable and potentially a Bluetooth-enabled smartphone to set it up. Modern Alternatives

Occasionally, third-party sellers list "Renewed" or old stock units, but these are becoming increasingly rare. What to Watch For

This is your best bet for finding a Fitbit One . You can often find them "New In Box" (NIB) or used. Prices vary wildly depending on condition, sometimes ranging from $50 to over $150 because of their cult-favorite status.