The Time-Stop Towers are devices used by the LEP to set up time stops. They function as a sort of rechargeable battery for generating the magical effect. Trained Warlocks feed their magic in the batteries and switch on the machines. The towers use the magic to generate the time stop field. An added bonus is that the technology used in the time-stop towers extends the duration of the time stop exponentially.
They were developed to prevent from using warlocks instead, as warlocks tended to show off, and would occasionally have to use the bathroom in the middle of a time stop.
The time stop was invented by San D'Klass who started the Santa Claus story. He made a time stop while humans slept and sent fairies to give them presents. Their intention was to lessen the humans greed.
In the first book, Commander Root combines the towers with the Bio Bomb as a last resort to annihilate Artemis Fowl and his cohort. Artemis escapes the time stop by changing his state of consciousness with ordinary sleeping pills.