The car alarm keeps going off on its own?

Being a 2008 they should be able to go into the security system and see what is turning it on. The common items are door and hood switches. There is a TSB out for that vehicle with this problem as well. It involves replacing the rubber bumper with a different one, so it hits the hood switch better. Hyundai TSB 09-BE-026

Technical service bulletin. IE something that the company has found that repairs a known problem. It basically says, we know this is a problem, here is a solution to it. In this case they know there is an issue with the hood bumper causing the alarm to go off because the hood switch doesn't depress fully and randomly sets off the alarm. The same issue you have, and knowing how many times vehicle alarms get tripped by bad or bent switches I would say it's very likely the problem.

The reason it doesn't go off when manually locked is that using the manual locks doesn't arm the anti-theft system. Nothing to do with the fob.

Leaning ON the hood closes the switch better, it is the same as if it had the longer bumper in the TSB. Release the hood with it armed and it goes off, the idea is to detect the hood or doors being opened. The problem listed in the TSB is that the switch normally is barely closed, as the car sets the body parts shift around and the switch opens. Manually unlocking or locking it doesn't turn the alarm on so it can't go off. Using the fob to lock it or unlock it doesn't disarm it. If you unlock it and then use the key in the ignition, that will disarm it.

It is a simple switch that is the common problem. An easy solution is to simply add some material to the rubber bumper that moves the switch. I've used the self stick felt or plastic floor protectors for it without an issue. Clean the bumper with some alcohol, let dry peel the backing and stick it in place. Like the attached but in lower quantities.

They may be closing fine but if they didn't pull up the TSBs they may have missed it, that is not uncommon. It's also possible that it is a door switch but usually you can look at the data and it will show what switch activated the alarm, So it would show something like LH Door active in the system. I'm just saying that it's a place to start. The other option is to put a data recorder in it and when it goes off it would record what was setting it off.

I would add the felt to the bumper and see if it stops going off. If it does you fixed it. If not then it's likely one of the door or the trunk switches. If it's one of the door switches and the doors are closing normally then the repair is usually replacing the latch assembly as the switch is inside the latch.

It is the switch, the hood has rubber bumpers and the hinges that support it at the corners. Then it has the switch mounted to the fender and the rubber bumper that pushes on the switch. That part is where the problem is, where the switch is. Doesn't matter that the hood is heavy, it matters that the switch can move and the hood doesn't push it far enough. But if you don't believe me or the factory who are both saying it is a known problem that they even issued a TSB for then so be it.

No, the hood shouldn't move if everything is like new. The switch is only an on/off switch. With the hood closed and latched it is supposed to open the switch and it should stay open until the hood opens about 3-4 inches. The problem is that the switch can be bent from the repeated opening and closing of the hood and when new the switch is set so it just barely opens which makes it harder for a thief to open the hood without setting off the alarm. If you open the hood you can see the switch bolted to the inner edge of the fender. The way you "adjust" them on other vehicles is to bend the entire mount up about 1/4-1/2 inch. On yours they used a better mount that doesn't bend as easily and they just changed to bumper to do the same thing. What I've found on most of the vehicles with this problem is that the repeated use of the hood and time has compressed the bumpers that normally hold the hood tight against the latch. Then the hood starts to have a small amount of play in the latch where you can lean on it and the hood pushes down and rises up maybe 1/4 inch. So you drive around and the normal bumps and potholes push the switch down and crush the various rubber parts. Now you park the car and it cools off and settles and the hood moves up from the spring pressure in the latch and the switch grounds out and the alarm goes off. It's a very common problem. The door switches are next because of the constant use of the doors.

That's usually what happens, you have a problem but it doesn't show up while in the shop.