There are only two tasks a safe provides. A specific amount of time it will protect its contents from a specific temperature and duration of said temperature in a fire. The fire rating is specific and easy to calculate if it will protect your guns based on how hot a structure fire gets, each one has variation due to size of structure and contents, but you can do a fair job with a little research to figure out how much fire rating you need for your positioning of safe in your home.
The second task is amount of additional time it take for "average" thief to access contents. Some thieves will find a gun safe by surprise and have to use the tools they find on hand in your home to open it. In another section on this site a person posted pics of his safe in his garage along with other firearms related toys relevant to the topic. Sitting within site of the safe was a welder. It would be easy to turn the welder up to its highest setting and use it to burn a hole in the side of the safe or cut the locking mechanism out if the thief thought the door was the weak spot to attack.
That brings up knowledge. Does the thief know the weak spot of a vault" Door is usually the strongest part as it is where most attacks happen. the sides and top of some vaults are very thin. Five minutes with an 18 volt cordless angle grinder and a cut off wheel will have you in and average gun vault. The best thing for the thief is the fire lining will protect the contents while he attacks it. Thus all a safe is designed to do is add time to the thieves attempt to take its contents. I consider in most circumstances the vaults as primarily fire protection. That is 75% of their job. The other 25% is to add enough time that a burglar cannot snatch, grab and run before the police or I dispatch from the alarm notification.
Most homes with alarms have standard 1-800-I-AM-SCARED alarms. The 1-800 company comes out and puts sensors on doors, windows, a couple of motions and a siren to alert the neighbors if they happen to care your home is screaming "help". They hook it into the phone line for monitoring and go on their merry way and send you a monthly bill. So here is the deal. Most homes now have a little NEMA waterproof box on the side of the house that the phone line comes in through. For a basic thief these days that has served 30 days or more or used a Google task bar knows that you cut that phone line. Then you look for the box with the siren and fill it full of expanding foam out of a spray can and once it swells up, the siren wont make enough sound to scare a squirrel in the attic.
My alarm is same as most others except it is all top line equipment and not 1-800-FREE-INSTALLATION quality although that beats nothing. There are two sirens, both hidden and face the neighbor on each side of the house. My alarm panel is hidden and gives 20 seconds to disarm. It also has a cellular backup hidden in the attic. If someone cuts the phone line it still has a way to call out. Also it has a radio backup that "polls" the alarm company at least once every minute. If the alarm companies computer goes three minutes without getting a ping from my house a technician accesses my alarm through the phone line to make sure all is well. If he can't access the panel from the phone line he tries via the cell module. If that is dead too, he assumes someone with knowledge has bypassed the alarm, dispatches the police and calls me and the wife. Once the extra 400.00 in equipment cost for these extras was spent, it adds a whopping 20.00 bucks a month for three types of monitoring.
I have three vaults bolted together side by side, bolted to the floor and bolted into a corner of my basement. That leaves the side of one vault and the tops of all three exposed. I built a steel locker that is the width and depth of all three safes out of 3/16" AR400 steel. All the doors of said cabinet have these:
http://www.allpadlocks.com/ez-catalog/X380790/92
The only difference is I replaced the lock cylinders with Mul-t-lock pick resistant cores that use a high security key. I also backed up the hardened bolts by tack welding the hasps at each corner. The entire unit was put on top of the vaults and bolted to each vault and the concrete wall behind. At this point all I had was one vault with one side exposed. That vault houses, cameras and such that I want protected but are not going to be life changing if they get gone. The guns stay in the center vault and one that is in the corner with two sides protected by concrete. The doors are 1/4" AR500 steel on my safes with active re-lockers and extra hardened anti drill plate over all of the locking mechanisms. The mechanical dials have keyed locks to keep anyone from spinning the dials without bypassing the wafer lock on the dial.
When installing a safe, remember that is bolted directly to concrete, condensation or any water that leaches between the safe and the concrete will rust the safe and compromise it. I chose a 3/8 thick laminate product to put under the safes and behind them so there was no direct contact with the concrete. I also used stainless fasteners for this purpose and used O-rings and silicone to help keep water intrusion from the fasteners.
The key thing for me is all of my heavy duty metal working equipment is at my business. Other than basic hand tools, a cordless drill, etc, there is noting on premises that gives a thief the tools to compromise the vaults without bringing them. If your vault is in your basement or garage where your welder and torches are, at least you have the fire protection if your home burns but please don't keep the tools to easily bypass your vault within site of the bad guys. I have seen it personally many times. Bottom line is this. A safe just adds time. According to the safe and the thief that time varies. If someone that knows what I do was coming for your stuff and you had an industry standard alarm and a 900.00 dollar or less safe, about 20 minutes and all your guns would be in their generic van that says Bills Plumbing so your neighbors just assume your toilet stopped up.
Keep the safe, keep the alarm. If you don't have both add them. Spend the extra 10 bucks a month for the cellular module and put a sensor on the safe itself. Install the safe in a corner so the back and one side have extra protection. Then, go as far as you want. If all you have are 3 long guns and 3 pistols, you don't need any more. If you have a prolific collection of investment grade collectibles, NFA class 2 & 3, or a dozen AR-15's then base your security measures in direct proportion to the value of your collection. If you own just one rifle and a couple of pistols you can skip the vault. Hide your rifle and tote your pistol when you leave the house then let the wife carry the other. If you NEED a safe, make sure to adequately protect your contents in proportion to value.
