Meet the Bad Elf 2300 GPS Pro+: a high performance GPS+GLONASS WAAS Receiver that enhances the capabilities of your iPhone. It provides barometric altitude for pilots and raw barometer readings for boaters. You can also use its USB connectivity to stream data directly to a PC or Mac. The battery lasts you 24 hours. There is no need for an internet connection or a monthly subscription to use this device. The Bad Elf 2300 GPS Pro+ sets you back $249.99 at this time.