the outside dimensions of the box are 14"x12" and it's 3.5" deep- and made as you guessed to fit between studs that are standard 16"OC. The lid is 16" wide and 14" tall to cover the box in it's entirety.
it straight up looks like a picture hanging on the wall.
weight wise, the box is no more than six pounds.. the cover/door is likely 10#, though. it uses euro style hidden hinges that allow about an 1/8th" lip over the hinged side, and plenty of overlap on the other three sides.
the weapon is held with a rubber coated magnet- I'll post pics here of the new interior when i get to one today, they're a bit different than the one in the image... far better.. i won't post it on instagram or FB because people straight up steal the idea and then accuse you of doing it... it's happened to me twice already.
the mechanism is 13.xxMzh RFID... the antenna, which is what opens it when it handshakes, is energized by a 'near' field of the device- meaning it doesn't need charging or batteries. the device will fail open when it runs through batteries instead of staying locked. two AA batteries will open the box something like 4k times according to the documentation provided, and will last two years idle according to the same documentation... i put old batteries in one which had just enough charge to open a few times, and then let it sit there for over a month and i'll be damned if they still didn't have enough power to open it.... i've yet to install batteries with enough energy to lock but not enough energy to stay locked yet- i'm still flirting with it trying to prove what is said. i DO know that if there is a battery removed the locks pop right open.
the antenna- i tried my level best to get RFID silicone rings like are popular for wedding ring stand in, and had long convo's with makers on producing them. i admire their honesty when they said "they just don't last" (the rings) "...as they bend they damage the antenna and they stop working.".... so... I have some silicone bracelets, the key fobs, a credit card sized key, and stickers that can stick to whatever (hopefully a rigid something).... they all work well... a straight up solid ring can be had- but i can't afford to stock stylish rings in various metals and sizes- they're about $90/ea for the precious metal ones that look decent, and i'd have to have likely 20 different sizes of just teh one make.... but what i MAY be able to do is provide a link for someone to order them through me to the maker and at basically cost if that's what they want (and it's what i want too)... not having to hide a 'key' and having it on your person at any given time is the whole point of these things. keeping weapons, prescriptions, ect, out of reach of kids is the other- but being able to get to them quickly and safely.....
