The FM Transmitter 2 allows one to send audio from any device with a headphone jack to a nearby stereo system or FM Radio. Some users use the transmitter with TVs, instruments, Echo devices, MP3 players, and more. It sends near-broadcast-quality stereo sound and features a 2-level LED indicator for optimal adjustments. It runs on a pair of AA batteries or an AC adapter and can fit in one's palm. It measures 3" x 3.5" x 1" and weighs 5.8 ounces. The Digital FM Transmitter 2 is also FCC Compliant. FM frequencies range between 88.3 MHz and 107.7 MHz.