Lumoback
You know you should sit with proper posture, but how do you know if you're actually doing so? By strapping on a Lumoback ($150), that's how. This wireless Bluetooth sensor is worn on your lower back, and gives you vibration feedback when you're slouching. In addition, it also connects to your iPhone or iPad, so you can track your activities throughout the day and get a more well-rounded picture of of how you — and your back — are doing.