As one of its daily deals, A4C offers the used Fitbit Charge 2 HR Wireless Activity Wristband in Black for $39.95 with free shipping. That's $40 less than our mention of a new unit from Black Friday weekend, $90 below the lowest price we could find for a new one today, and the best deal we've seen for this tracker in any condition. It tracks steps, distance, sleep, and calories and features an OLED display with clock, continuous heart rate monitoring, multi-sport modes, Bluetooth 4.0, smartphone notifications, wireless sync with supported computers and smartphones, and a battery life of up to five days. It's available in size S only. Deal ends today.