Get a good tool and drill-resistant fire safe from a good supplier - there’s a surprisingly strong second-hand market - and as
@STANDY says, make sure it is too heavy for three people to lift, bolt it to the floor where it isn’t against an outside wall,
adding that
ideally such a safe is installed such that all 5 sides (other than door) are not accessible. Safe’s security ratings are largely based on the security of the
door side of the safe, with the other sides being relatively vulnerable.
for example, here’s the relevant performance standards of a true “safe”, in this case a “TL-30” rated safe (my emphasis added below) - which is a common version of a home safe with a relatively high security rating
:
“U.L. LABEL - BURGLARY CLASSIFICATION TL-30: SUPERIOR PROTECTION
Signifies a combination-locked safe designed to offer a maximum
door protection against attack by common mechanical and electrical hand tools and any combination of these means….
Performance Requirements
The
door successfully resist entry* for a net working time of 30 minutes when attacked with common hand tools, picking tools, mechanical or portable electric tools, grinding points, carbide drills and pressure applying devices or mechanisms, abrasive cutting wheels and power saws.
* Entry means for: Opening
the door or making a 6 square inch opening entirely
through the door or front face”
Here’s what one might expect a TL-30 to look like, noting both the depth and construction of the door thickness vs the walls, but also the interior space provided (given the thinness of the other 5 walls):
Safes such as the TL-30 sized above may cost $2,000-$6,000 new for such a high door rating, weigh 1,400 pounds, and provide relatively ample interior space (compared to the safe’s overall volume) with the outside dimensions of the above safe being 38 x 38 x 33½ but and with the inside dimensions being 36 x 36 x 26
In contrast, here’s a comparably sized but more “commercial”/“industrial” rated “TL-30x6” safe, intended to provide security on all 6 sides, which new may cost upwards of $15,000 and weigh 5,000 pounds, with the outside dimensions of this safe at 38W x 35D x 41H, with the inside dimensions being 27W x 16 1/2D x 30H
Both of above stand in contrast to almost everything sold at sporting goods stores, which technically aren’t safes but instead “residential security cabinets” - those things, the 5 non door sides can be popped open like a tuna can with any sawzall
Which is all to say: almost any safe a person would consider (or afford) for home, no matter how heavy, is intended to be installed to disallow access (even brute force access) to anything but the front door.
Which is a mistake made by the guy in the video we’ve been discussing - the thieves just took a torch to the top side
