We've been hearing about cochlear implants of various sorts some time for some time now, but it looks things are about to get a whole lot more implantable, with a pair of fully implantable hearing aids now in clinical trials. One of those is developed by the folks at Envoy Medical, while the other comes from Otologics of Boulder, CO, which the MIT Technology Review got to check it out first hand, so to speak. Dubbed "Carina," the hearing aid consists of four separate pieces that are designed to be countersunk into the skull, including a microphone the size of a fingernail that sits behind the ear and a main processing unit that also houses the rechargeable lithium-ion battery that powers the device. That, as you're no doubt wondering, gets replenished by a charging unit that's held in place with a magnet and must be worn for an hour or two a day. As the Review heard straight from one of the device's early users, the entire setup appears to work remarkably well, delivering a "natural feeling of hearing." As it's quick to point out, however, the device still has a long ways to go, with the study currently only having twelve of the 70 to 80 users it needs to complete "phase II" of the trials. And, of course, there's that small matter of price, with the Carina currently ringing in at a cool $20,000 (for one ear), none of which is covered by insurance.