Foxconn has demonstrated an iPhone-compatible smart watch, which it plans to release on its own as an iOS accessory. The watch can measure vital signs, as well as check phone calls and Facebook posts. Though other iOS-compatible Bluetooth smart watches have already been released — such as Martian’s Passport Watch, ConnecteDevice’s Cookoo and Pebble — Foxconn’s watch is notable because the company has been Apple’s key manufacturing…