You're confusing *unlicensed* with *legal* I think. It is not allowed to make an intentional radiator, even an unlicensed one, that hasn't been certified to comply with FCC Part 15 limits for the frequency it uses.

More here: [www.arrl.org/part-15-radio-frequency-devices][1]


  [1]: http://www.arrl.org/part-15-radio-frequency-devices

From this doc:

"Low-power intentional radiators: Part 15 rules also permit intentional radiators to operate on nearly any frequency. These low-power intentional radiators are limited to specific field strengths that vary with frequency. The field-strength limits were chosen so that interference is not expected under most circumstances. **These devices are certificated**."

As far as enforcement of such things, it's kind of the 'honor system' when it comes to interference. You're not allowed to make a radiator that interferes with someone else's stuff. If you do, and they call you on it, you are obliged to stop using your interferer.

As a practical matter, something powered from a 9V battery using a 'garbage' band like CB or one of the other unlicensed bands that emits less than 50mW is unlikely to encounter problems.