Spell Key

Spell keys were part of the archano-tech revolution that rapidly brought the alliance into the industrial age, from the steel age, in a single generation. Spell keys are magical devices that store, and repeatedly emit the same energies of the spell it was 'keyed to' for as long as it has energy to do so. In practical terms this can be from making a fire key, used in appliances or home heaters to generate heat in cold weather, to healing keys, able to generate a healing magical aura proportional to the raw energy applied to it.
Spell Keys are the foundation of most modern amenities and equipment. Automotons used for security are an example of a large cluster of Spell Keys being put to use in a single unit. Repair keys for maintenance and damage repair in case it takes weapons fire. Various Keys to allow it to shock or stun to subdue trespassers without harming them, or light keys to emit lethal beams of death in cases that call for it.
And, with more advancement, it was discovered that it wasn't necessary to have magical energy to run them. Over time they discovered the ability to harness electrical generation to power up the spell keys. This made them far more widely available as it wasn't required to have an elf power them up anymore. Now anyone could. They just needed an energy source. And much experimentation was done to find the best and most efficient ways of creating said electricity. As the ease of creation and usefulness because widely known, so did it's demand. And demand for power. Why break your break chopping firewood, when you could simply use a fire spell key to heat your house to a uniformly comfortable level.
Advancement and experimentation continued right up until the final day of the war. With the Spell Keys, once created and lauded as being a marvel for making lives easier, now regularly being used to great and terrible effect for the war effort.

Mechanics & Inner Workings

The spell key resonates the spell is was 'keyed' to, thus continuously radiates the magical properties that the spell would do. Although, depending on the key, it may require additional outside power for it to really be effective, otherwise it could eventually burn out and become useless. Which it has a chance to do anyway.

Significance

Had been made and incorporated into nearly every type of item imaginable. The more they were used the more potential for use was discovered. Which lead to even more advancement. Rapidly.

Rarity

Hard to produce since the war, and currently mostly just salvaged. The only ones capable of making them are the elves.