At the risk of once again being the voice of dissent, I have to say that unless you show me a FCC CFR part xxx paragraph that states emissions below a certain power level are uncontrolled at that frequency in the U.S. when transmitted by an uncertified device then they ARE. I know of no such definition of "low power". FCC CFR part 15 and part 18 list the requirements to have a certifiable device design to submit to the FCC for an FCC ID # for the end user to be exempt from licensing. Just because YOU think you meet those requirements does NOT mean you can use your device without either user licensing or device certification. That's up to the FCC. You may use a hobby 315Mhz transmit module for years without any complaints from licensed users of that band or may immediately be reported to the FCC, as was the gentleman who according to the FCC's enforcement webpage imported and used 434Mhz wireless links in the U.S and was fined $11,000. Note that 434 MHZ is one of the freq that sparkfun sells; (and in the U.S. is regulated for licensed amateur use). And that's just the tip of the iceberg. Over and above the hardware requirements (frequency, power level, bandwidth, spectral purity) there are band restrictions for the type of modulation (AM,FM, PSK, OOK,) and whether the transmission is phone(voice) or data authorized on that frequency.
for more info on those who thought they didn't need approval to transmit see:
http://www.fcc.gov/eb/Welcome.html
http://www.fcc.gov/eb/Orders/2005/DA-05-2394A1.html
the FCC is prosecutor, judge and jury in these cases.
...and here's a little chunk of a typical FCC "notice of apparent liability" (aka NAL)
10. In his response to the NAL, Mr. Grover again admits that he operated a
radio station on 87.9 MHz from Lakeland, Florida, but states that he
did not intend to violate the Rules. Mr. Grover states that he thought
he was operating a low power FM station pursuant to Part 15 of the
Rules. However, because he did not use equipment certified for Part 15
use, Mr. Grover states he was unaware that his station exceeded the
allowable Part 15 output power. Mr. Grover also states he had no way
to verify that his equipment was set at the proper output power.
11. Although Mr. Grover states he believed no license was necessary to
operate his station, that belief was mistaken. Part 15 of the Rules
sets forth conditions under which intentional radiators may operate
without an individual license. However, if intentional radiators fail
to comply with all of the applicable conditions set forth in Part 15
of the Rules, they are not authorized to operate in the United States
without a license. Mr. Grover admits that he did not use a transmitter
certified for Part 15 use and that he exceeded the allowable Part 15
output power. Accordingly, his operations were not consistent with the
requirements of Part 15 and were unlicensed. Moreover, his belief that
his actions did not violate the Act is irrelevant as to whether his
violation was willful, as he intentionally operated the station. Thus,
based on the evidence before us, we find that Mr. Grover willfully and
repeatedly violated Section 301 of the Act by operating radio
transmission apparatus without a license on October 2 and 7, and
November 6 and 7, 2008.
If you think saying well sparkfun sold them to me, or a guy on a internet forum said it would be OK because it was "low power" is a viable defense, good luck to you on that. And while an output power level that gets someones attention is the usual cause for investigation as it can be done outside your property, Output power is NOT the only criteria for Part 15 (or 18) compliance. Hence using CERTIFIED part 15 devices.
-curious people shouldn't get too attached to their cat. ;-(
