But if you didn't move, or re-org your room or closet, then the obvious, the so-called "usual suspects", do indeed immediately and sadly come to mind. Frankly, given it's rising cost, it may be in your best interest now to build, or have built, a simple plywood chest with a padlock or two on it, to more safely store your valuable ammo and even perhaps a previously and "legally unsafely stored" handgun or three. You can even lag-bolt such a chest into your closet floor, which makes it triply hard to just lug off with a hand ruck.
Yeah, it could also be somewhat easily broken into, but any of your "friends" or possible roommates would also have to make quite a lot of noise, and also make quite a mess with big-time evidence you'd notice quite soon after it happened. You could also fit it with a simple key-armed (visible on the outside for additional emotional dissuasion) alarm system that howls loudly {130 dB let's say; in other words, painful!) from an internal horn that is also hard to get at immediately!
As well, if you fit the inside corners with blind-bolted and/or epoxied-into-place angled steel, even the thinner stuff, and also epoxy-glue the wooden corners, it makes for quite an effort to dissemble this war chest, and those efforts also prevent anyone from just quickly and easily prying it open.
As well, if you don't have a good steel safe (which, in today's litigious society, is more than just a good idea... esp, if one of your firearms is stolen and then used to harm or kill someone!) you an use it in the interim as an impromptu gun safe.
I am personally changing all my ammo storage arrangements given the rising cost and growing scarcity of ammo. I literally can't afford to have mine stolen with no way now to easily replace it!
Well, even as regards ammo, Molon Labe, so to speak!