LUMOback - $149

LUMOback is a wearable posture sensor & mobile app system made to support
healthy backs. 

LUMOback is highly sensitive at measuring lower back spinal posture. In most
cases, poor lower back posture such as slouching, leads to poor neck and
upper back posture. 

Worn around the waist, the LUMOback posture sensor gently vibrates when you
slouch from your lower back, reminding you to sit or stand straight.  

Combined with the LUMOback smartphone application, LUMOback can track your
progress and activity levels and help you improve over time. 

LUMOback website
http://www.lumoback.com/