Ah, okay... gotcha that your son is still a baby. But, I think it's safe to presume that at some point he's going to move into his own room, because as he matures into a child you're not going to need to watch him as much. As he matures and becomes more independent, he'll be alone more often. Yes?
My son is 3. He walks around the house and is fairly independent inside the house. He may choose to play in his room, in the living room, pretty much most of the house except the garage and our bed room. We do not follow him around every time he changes from one room to the next. We also do not leave guns out, loaded or otherwise... because he may find them and he does not have the judgement at 3 for us to be sure that he won't play with the gun, possibly shooting it, etc. So they stay in the safe. Toys on the other hand, such as squirt guns, he has access to.
Toys, such as squirt guns, have a different nature than tools, such as firearms. There is a reason why kids can play with one and not the other. Don't try to complicate things by introducing child shooting cops into this, because that's an entirely different subject. A real gun doesn't need a third party to make it dangerous. A child playing with it can kill himself. A child playing with a squirtgun (and before you go nuts and try to talk about a squirt gun filled with acid or some crazy thing, no it's just water) by himself will not accidentally kill himself.
Tools have a different nature than toys. This is why guns need to be kept from kids (or in the case of older kids, supervised) and toys do not. This nature is what I am calling dangerous. If you don't like that word, lets hear your better description of the difference between a tool, such as a firearm and a toy, such as a squirtgun.