Strongbox

Strongboxes are items that appear in. They are the method of obtaining Weapons and Armor, rather than buying weapons like in previous games. You can find strongboxes in various locations throughout the game, but they are primarily located in secret rooms and can be obtained from killing bosses. Multiple bosses do not give multiple strongboxes, and the amount of strongboxes obtained from a boss at the end of a mission is limited to one. Additionally, objects like vases in the VIP Mission can contain loot drops, including strongboxes. Killing zombies also has a small chance of dropping strongboxes, and collecting a Daily Reward may also award strongboxes.

Tiers of Strongboxes
There are nine tiers of Strongboxes you can find. In order from lowest to highest tier, they are:
 * 1) Steel
 * 2) Titanium
 * 3) Molybdenum
 * 4) Iridium
 * 5) Neodymium
 * 6) Promethium
 * 7) Thulium
 * 8) Nantonium
 * 9) Black (PC only)

Properties

 * Each Strongbox opened contains exactly one weapon or armor piece.
 * The higher level the strongbox, the better items you'll get. That does not mean that lower-tier Strongboxes will always give undesirable items, and that does not mean that higher-tier Strongboxes will always contain something desirable to the player. It is still possible to get high ranked items from low level boxes. E.g it is still possible to get an empty 10*** [RED] RIA 20 Striker from a Steel Strongbox, though the possibilities are higher during late game.
 * The higher level the strongbox, the more "flash" you'll see from collecting the box in a mission.
 * When obtaining a relatively good piece of gear from a strongbox, as in having an augment level of 8 and up, the interface will flash lightning twice in rapid succession and display the text "HIGH LEVEL GEAR!" in the upper-right-hand corner.

Black Strongbox
A ninth Strongbox was added into the game in the February 3rd update of 2015, which can only be opened with a Black Key. There is a small chance of obtaining a Black Key via a Nantonium Strongbox in Nightmare Mode, although they can also be obtained via rewards or be bought in the store for 20 kreds/NK coins. Additionally, there is a chance of getting one as a reward for completing Events; if the player is in the Diamond tier, they'll have a 10% chance, Platinum a 4% chance, and Gold a 0.5% chance.

Black strongboxes contain a Black weapon/armor.

Also, unlike other strongboxes where players can just accumulate as many as they want, the player is only allowed to have a maximum of 5 Black Strongboxes and any more must be discarded.

Related Achievements

 * For Me?
 * Boxer
 * Most Toys Wins

Trivia

 * The Steel and possibly Promethium, Thulium and Nantonium strongboxes are the only ones colored like the material they are made from.
 * Titanium strongboxes are green when it is actually silver-colored, Molybdenum strongboxes are blue when it is really gray, Iridium strongboxes are blue when it's actually silver-colored, Neodymium and Promethium strongboxes are purple when Neodymium is actually silver and Promethium's color is a silvery-white, though in some forms, it's a blue-green glow, and Nantonium strongboxes are bright yellow, but its true color is unknown due to Nantonium being fictional.
 * All element-metals are silver/grey in color apart from gold and copper. The Strongboxes made from a pure element are all except Steel and Nantonium
 * There is, however, a possibility that Nantonium is naturally silver-white. An NK game called Magnetic Defense features a special item called "Nantonium Ball". It is a large, silver-white sphere. Apparently, Nantonium is very resilient, as the Nantonium Ball on Magnetic Defense can easily plow right through long lines of tanks.
 * Neodymium and Molybdenum are the only strongboxes to have their own special light color, as Thulium and Iridium share a greenish light, Nantonium and titanium share yellow, and Promethium and Steel share white, with Neodymium having purple lights and Molybdenum has light blue lights.
 * If you look on the atomic number in the periodic table of elements, the iridium box should have the number 7 while the others (Neodymium, Promethium and Thulium) should have a tier less.
 * The mobile Version for SAS 4 does not have the same graphics for the strongboxes; instead they look more saturated in color and only have lights seen from the sides and not on top.
 * Black strongboxes have the Black logo on top.