Force fields provide protection from projectiles, energy-based weapons and electronic surveillance. Upon impact of external objects, the effect varies. Against personal force fields, bullets simply bounce off and fall. Explosive weaponry such as missiles against ships is more spectacular however, the absorbed energy creating a corona effect. The only sign of a force field deactivating is a slight ripple through the air around it.
They are useless against cloaked opponents, since they only react to things they detect.
By 2499 longer-lasting portable devices had been developed for personnel, such as containment fields for firebats. These were virtually immune to small arms fire and, at full power, provided some protection from debris.
Force fields can protect parts of buildings. This version of the force field also existed as of 2478.
By 2491 force fields could also be mounted on battlecruisers and Wraiths. Battlecruiser shields hog energy and are only used when a battlecruiser is vulnerable, such as when coming out of warp space, entering a planetary atmosphere or in combat situations. With enough power, a battlecruiser's shields can expand beyond the ship itself, generating a halo effect that will protect ships that fall within it. However, the larger the area a shield covers, the less effective it is. Force fields can also be used to shelter docking bays from the vacuum of space.
Following the Brood War remnants of the Confederacy undertook some work into "polarity shifting energy shields using battlecruiser technology." In addition, force fields were able to be applied to small scale objects such as cabinets, acting as a means of security.
The Terran Dominion used force fields to protect an advanced munitions factory on New Sydney. It was occupied by a Koprulu Liberation Front cell, which used the force fields to protect themselves. However, the force fields only protected against opponents it could detect; it wasn't able to detect ghost agent Nova.