I leave my solar charger battery pack in my car with my dashcam. Nothing ever seems to happen. Guess it just depends on the region of the country you live in. I even leave my sunroof open all the way sometimes when I go to the grocery store.
An alarm has almost nothing to do with it. Alarms are mostly for making noise after something bad has already happened. The better ones can do more, but are mostly for making noise when nothing has happened. The massive inconvenience of having to deal with my wallet being stolen, and the long term identity impacts are enough for me to never leave my wallet in my car.
For everything else, it is out of sight out of mind. But there is risk in moving everything to the hatch area if you move it all when you arrive at your destination. Several colleagues had laptops stolen. It was pretty easy to figure out that someone in the parking structure was watching them stash their stuff. Each one had moved their valuables to the trunk in the structure, and they were the only cars broken into. Leaving valuables visible is just asking for a broken window too.
A couple of thieves working in my area recently came up with a scam that limited alarm problems too. They would drive through a neighborhood and break a window in nearly every car on the street with a pellet gun. Hours after the ensuing attention that arose from alarms and the noise they would return and steal everything. The plan was kind of smart, using the same trick over and over wasn't. They were sentenced a few weeks ago.