Does my Arduino-based device need FCC certification?

You are confusing certification and emissions requirements. Only intentional radiators need to be certified. From your description, your device is not a intentional radiator.

However, you are still obligated to ensure it does not radiate excessively. The limits are defined in part 15 of the FCC rules.

How you determine for yourself and ensure that the device does not radiate more than allowed is up to you. The FCC doesn't go looking at the millions of devices that are unintentional radiators and test them for compliance. However, your competitors might. If they find your device radiates illegally, they can file a complaint with the FCC.

The worst case is if some communication got interfered with, the FCC investigates, and finds one of your devices causing the problem. Then it gets serious fast.

Large resellers may require a recognized lab to certify that your device radiates legally, or they won't carry it.

All that said, for a little guy selling a few 100 gizmos a year off some web site, there is very little chance anyone is going to check whether the device radiates within the limits. If you follow best practices, like a good overall grounding strategy, filtering of external wires, etc, chances are very low your device will radiate enough past the limits for anyone to notice or to care.

As Dirty Harry would say: "you've got to ask yourself one question: 'Do I feel lucky?' Well, do ya, punk?"

Code of Federal Regulations, Title 47, Part 15 (47 CFR 15) of Federal Communications Commission (FCC) rules and regulations regarding unlicensed transmissions. Nearly every electronics devices sold inside the United States radiates unintentional emissions, and must be reviewed to comply with Part 15 before it can be advertised or sold in the US market.

The verification procedure requires that tests be performed on the device to be authorized. These tests measure the levels of radio frequency energy that are radiated by the device into the open air or conducted by the device onto the power lines. After these tests are performed, a report must be produced showing the test procedure, the test results, and some additional information about the device including design drawings. The specific information that must be included in a verification report is detailed in Part 2 of the FCC Rules. Sections 2.951 through 2.957 Once the report is completed, the manufacturer (or importer for an imported device) is required to keep a copy of it on file as evidence that the device meets the technical standards in Part 15. The manufacturer (importer) must be able to produce this report on short notice should the FCC ever request it.

There is no filing with the FCC required for verified equipment.

There are a number of exemptions outlined but not limited to the following:

EXEMPT "Test equipment" includes devices used for maintenance, research, evaluation, simulation and other analytical or scientific applications in areas such as industrial plants, public utilities, hospitals, universities, laboratories, automotive service centers and electronic repair shops.

Suggestions

Something that pulses once a second could easily go under the radar of scanning Sweep tests. So you ought to minimize the unintended radiation with twisted pairs, CM chokes and or snubbers so that it cannot be hear on an AM radio 30m away on a weak channel.

You will require an emissions certification for your product. The certification process would include your complete product in it's enclosure and would have to be tested with any normal accessories like an AC adapter attached. It is also typical that representative cables must be plugged into all interface connectors that would normally be used during operation of the device.

If your device is operated off the mains power line you have to undergo additional certifications for conducted emissions and immunity to certain applied disturbances like electrical spikes and surges.

There also requirements for your product to be tested for immunity to static discharge. Safety testing may also be required depending on the product category and customer /user location.

The fines and potential liability claims can be considerable if you do not follow the rules and would most certainly be far in excess the cost of having certification done.