Isn't it illegal to transmit FM without an FCC license?
Or maybe there's a certain power level you can stay below & stay legal.
Normally yes, but these types of devices are allowed to transmit through "Part 15". The power level is very low. I believe the regs(/laws) are worded in such a way that it factors in antenna design, so you can't use a super duper antenna to increase your range.
Keith