And there's ISM bands as well. However, all of these unlicensed bands have strict limits.

For any of the fun stuff, you need an amateur radio license :-)

> However, all of these unlicensed bands have strict limits.

This is absolutely key here - even in unlicensed bands one cannot just start using the spectrum without careful consideration of regulations for that spectrum.

When I was working in the 902-928 Mhz (FCC and similar) and 860s (for ETSI) for RFID we had to do a lot of work to ensure our transmit power, power ramp up, frequency hopping and listen before talk were all implemented properly and demonstrable for certification. It was not trivial.