Killswitch

The killswitch has several functions. One is to destroy evidence of an agent when they are killed and damaging any hostiles who are around. Its other function is security, if an agent goes AWOL then someone at UNATCO can say a phrase and it explodes the agent.

Nano-augmented agents have a similar killswitch. The main diferences are that it doesnt blow up the agent and it take around 24 hours to kill the agent, while older killswitches are instant. The way that the nano-augmented killswitch works is the nanites are programmed to go into exponentional growth.

It is subtly revealed throughout the story of Deus Ex that Paul and JC both have the Gray Death, and ultimately that their nano-augmentations ARE the Gray Death. As such it is clear that their killswitches amount to making them suffer the same symptoms as any victim of the Gray Death.

The phrase "Flatlander Women" is Agent Anna Navarre's killphrase which is analogue to the nano-tech function of a killswitch