Quell, a wearable neurostimulator developed by Waltham, MA-based NeuroMetrix, is intended to provide relief for users who suffer chronic pain due to conditions including fibromyalgia, sciatica, post herpatic neuralgia, and neuropathy. The device uses an electrode strapped to the upper calf to deliver pulses that trigger a pain relief response in the brain. It can also measure the quality of users' sleep. Quell is FDA approved as a Class II medical device and will be available to consumers over the counter starting in the second quarter of 2015.