alt Hacker News> Here in Germany you have to be careful when setting up a homemade radio signal - it might be illegal depending on frequency and transmit power.
In Germany and everywhere else. The difference is how much it's enforced.
Note that this project isn't using that horrible Raspberry Pi GPIO PWM hack that shits all over RF but an off-the-shelf low power car FM transmitter product. I guess if someone knocks on your door you can point your finger to whoever in Germany sold you that.
At least in the U.S., it's a complete non-issue for an output power that can easily cover the size of a wedding reception as long as you're not using a wide-band transceiver.
You'll want to be "kind" to the extant spectrum and do a responsible frequency sweep to select the "quietest band" prior to broadcasting. And you'll only want to broadcast during the event itself.
The FCC has better things to do than to try and track down an ephemeral milliwatt infringer.