You're confusing *unlicensed* with *legal* I think. It is not allowed to make and use 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, and that emits less than 50mW or so is unlikely to encounter problems.