The ForceField.
This Personal Forcefield is a device developed by the TSC, similar to the ones used by the aliens.
Archangel gave it to the Commander first, in order to protect him for a possible attack by the West Coast chapter of the Brotherhood of Steel during his speech in Rivet City.
After this event, a device that recharged the force field was placed in the Commander's Quarters.
The protection can be activated with the Strange Emblem.