The sequel to last summer's Pulse Activity Tracker, Pulse O2 ($120) is the newest health accessory from Withings. Virtually identical in nearly every way to the last version, the extra $20 added to the price tag and O2 added to the name coincide with two new features. The most notable is the ability to detect blood oxygen levels, which is especially important for mountain climbers, those training in high altitudes, and people with breathing problems.…
