In the US you may broadcast FM with a Part 15 device limited to about 200 ft (61 meters.) However, finding such devices and transmitter ICs is becoming rare as

In the US you may broadcast FM with a Part 15 device limited to about 200 ft (61 meters.) However, finding such devices and transmitter ICs is becoming rare as this device market has mostly transitioned to Bluetooth. Low Power FM requires a FCC license and appears to be stagnant with no licenses granted since 2013. https://www.fcc.gov/media/radio/low-power-radio-general-information https://www.fcc.gov/media/radio/low-power-radio-general-info...