[Max-q]

Is it legal to sell a device with radio in the US without FCC certification?

In the EU it's illegal to sell without external certification if the product is a medical device, is made for children or contains a radio.

Certification will typically cost you $5,000-$15,000 depending on which lab you use.

[nhwangus]

EE here - he technically has to comply with FCC Part B since he's selling in the US. That said, the hobbyist keyboard community has been pulling this for a while for small group orders without issues. Pre-certified modules are helpful, but stuff gets weird when it's on a board, so no guarantees. The fact that it's on a single layer board doesn't instill confidence since that typically means less than ideal return paths that can cause problems.

[littlestymaar]

How does that works if you're just reusing off the shelf bluetooth component? (that's likely already certified)

[enderfusion]

Off the shelf radio module, ain't nobody got time for certs.

[numpad0]

Modules like ESP32-WROOM, Seeed XIAO ESP32C3, and ES2810AA2 comes certified, re-certifications should not be needed(IANAL).

[rnewme]

I believe that to be true (at least for the European market), however you do need to have the manufacturers documentation on it!