Auto Insurance

I don't think auto insurance pays for the unit. If that was true, then auto insurance would have to pay for everything else inside the car.

Depending on your policy, it probably would be. My sister got paid for her CD collection being stolen out of her car when it was broken into.

I believe that your homeowners policy is the one that covers any of your property stolen from your car.

Some homeowners policies will cover stolen car contents, some auto policies will - if one wants to make sure their unit is covered, all they need do is see their insurance agent, who would be more than happy to sell them a policy that will cover their GPSr.

Has been that homeowners (to include renters insurance) policy covered contents of a stolen vehicle. I had a pickup with a slide-in overhead (fancy) camper and 17' canoe stolen, years ago.
All the camping equipment, fishing gear, tools, etc inside the vehicle or camper were covered by my renters insurance. When I bought a house I asked a hypothetical question and was told my homeowners policy would cover anything like that again.

I'd also take kch's suggestion and check with your agent to make sure.
Electronic equipment is sometimes a "touchy" subject with insurance claims.