As one of its daily deals, Amazon offers the Lumo Lift Posture and Activity Tracker for iOS / Android, model no. LLK020-001W, for $49.99 with free shipping. That's tied with last month's mention and the lowest total price we could find by $29. This sensor features Bluetooth 4.0 and tracks posture, steps, distance, and calories burned. It requires either the iOS app or the Android app. (Note that then Android app is in Beta and is not compatible with all Android devices.) Deal ends today.