They also provide a lot of EFIS (Electric Flight Information System, or "Glass Cockpit") for small GA aircraft. I think AeroDyne and Honeywell are also in this market but I mainly see Garmin there. Like the G1000 (higher models are available on business jets I think).
It's pretty good too, you get a lot of features that were limited to airliners in the past. Like seeing terrain contours around you. Not that I fly IFR (instrument without visibility conditions) but still. I think it's very impressive.
They have really become the gold standard in avionics, so much so that some airframes are preferred to others due to the fact that they've chosen to integrate a Garmin flight deck instead of Honeywell/Rockwell/etc. They have a very consistent and capable design methodology that extends from single engine piston avionics all the way up through relatively large GA jets.
They've also made advances with their Autoland product, which can take control of a small aircraft and safely land at an airfield while communicating with ATC.
The C172 with a G1000 setup was around $20/hr more at the local flight school than a C172 with a six pack. Def not needed for X-country but I always felt safer flying it through busy airspace. Garmin really does make fantastic avionics.
But the margins on that business are not exceptional. Operating income on "outdoor" segment of their business, the one that includes the epix and fenix series watches and so forth, is higher than aviation segment.
Margin isn't everything, it's a very stable business with a very wide technological and regulatory moat. Add to that fierce brand loyalty among pilots and it's a great business IMO.
Personal electronics (unless you are Apple basically) is a pretty fickle business and fortunes can change very rapidly. Aviation? Not so much, unless you chuck a Boeing.
It's pretty good too, you get a lot of features that were limited to airliners in the past. Like seeing terrain contours around you. Not that I fly IFR (instrument without visibility conditions) but still. I think it's very impressive.