You are correct, and right now it is complicated.
Many but not all US states regulate medical device manufacturers. What is worse, it is not always the same agency in each state which does the regulating, and the laws can be very different. This grew out of regulation of drug distributors and also in part because some states feel that the FDA is not providing sufficient oversight to device manufacturers.
DISCLAIMER: The list below is not complete, I am currently working on getting a comprehensive list but this often involves calling people at various states for clarification so I am ab out halfway through. Also it is subject to change as the laws of individual states can also change.
A few states currently do not regulate device manufacturers:
VT, NY, OH, NM, MN, ND, OR
Some states have establishment regiatration for device manufacturers only if they are located in-state:
TX, GA, MA, PA, NH
Some states require a separate license if the device manufacturer sells directly to patients:
MS, GA, NH, NV
MO requires a license if the company is selling to anyone
other than patients.
Some states require a license if the manufacturer's products are distrubuted into the state in any way:
LA, ID, NH, CT
Most states require registration and/or permit if the device contains a drug.
Many states require a permit if the device is considered DME and the company is selling to patients.
In some cases it makes a difference if the device manufacturer uses a distributor, in some cases it doesn't.
States generally use the term "Legend device" to describe the type of device which they regulate. This term refers to the "legend" present on devices cleared by the FDA "
Caution: Federal Law (USA) restricts this device to sale by or on the order of a physician"
If you want to check whether a state regulates medical device manufacturers, try looking for the state "Board of Pharmacy" since this is most often the agency responsible for registration, permitting and licensing.
Also a very good resource can be found here:
http://www.hida.org/AM/Template.cfm?Section=Home&TEMPLATE=/CM/ContentDisplay.cfm&CONTENTID=13594
But be careful, as of today this report is 18 months old and a lot can change. OR for example has proposed a law requiring all prescription device manufacturers to register, so this state can go from no registration to required registration overnight at any day.
Edited to add:
I also find this list helpful as a starting point to find the state agencies that might be responsible for licensing and permitting medical device manufacturers. It applies to drugs, but most often whichever agency regulates drug distributors and manufacturers also regulates device manufacturers and distributors.
http://www.sentrybps.com/gmp-facility/licenses_and_registrations/
Disclaimer: I have no affiliation with any company or organization associated with the links posted.