So your attitude to legality is just governed by your chance of detection? Not the potential life threatening consequences of interfering with emergency services, life support systems and the rest. What a nice chap you are.
Unlicensed operation on the AM and FM radio broadcast bands is permitted for some extremely low powered devices covered under Part 15 of the FCC's rules. On FM frequencies, these devices are limited to an effective service range of approximately 200 feet (61 meters). See 47 CFR (Code of Federal Regulations) Section 15.239, and the July 24, 1991 Public Notice. On the AM broadcast band, these devices are limited to an effective service range of approximately 200 feet (61 meters). See 47 CFR Sections 15.207, 15.209, 15.219, and 15.221. These devices must accept any interference caused by any other operation, which may further limit the effective service range.
and I imagine that a similar situation holds true in many other countries
Radiocommunications (Low Interference Potential Devices) Class Licence 2000(1) This Class Licence authorises a person to operate a transmitter included in a class of transmitters mentioned in item in Schedule 1, subject to the following conditions:(a) the transmitter must be operated:(i) on a frequency, or within a range of frequencies, mentioned inthe item; and(ii) at a radiated power that does not exceed the maximum EIRPmentioned in the item; and(iii) within the limitations (if any) mentioned in the item;(b) the transmitter's operation must not cause interference to the operationof radiocommunications services.-----------Schedule 1 TransmittersItem 21: Wireless audio transmitters and auditory assistance transmittersFreq: 88-108 MhzMax EIRP: 10uW
New Zealand residents are allowed to broadcast licence free-of-charge at a maximum of 1 watt EIRP in the FM guardbands from 87.6 to 88.3 and from 106.7 to 107.7 MHz under a General User Radio License (GURL), which is issued by Radio Spectrum Management, managed by the Ministry of Economic Development.
Exemptions from licensingDeregulation is an important aim where this can be done without damage to licensed use. Much radio apparatus is therefore exempted from licensing, including: : :e) a wide range of short range devices, including certain low power FM transmitters (sometimes called 'car baby' devices), which wirelessly connect MP3 players and other personal audio devices to radios and in-car entertainment systems.