Whilst the Theremin Proximity Alarm is purely an alert for further security measures, the En Garde Security Post takes the proximity field technology of the Theremin Alarm and develops it with its own defensive system to prevent breaches of the field. The En Garde system requires structural installation in a building, usually taking the form of a frame around the feature it is protecting, usually either a door, window, safe, picture or display. Dividing the area of the field between paired ports (normally either into halves or quadrants) the proximity field informs a dedicated babbage engine that instructs pneumatic arms. The arms are normally sheathed within the ports of the frame (again, the ports are normally disuguised as architectural features) but upon activation the arms spring forth wielding rapiers (although varient systems carry different weaponry) ready to engage any intruders within the area of the field.

The security post can be set to one of three settings. At its lowest setting the arms simply use the blades to block further progression into the area of the field; The mid setting will attempt to disable any threat within the field and the highest setting is lethal and engages a further development within the detection field. Using a highly sensitive audio-receptor the babbage engine is able to detect and locate the presence of a heartbeat, the babbage engine is programmed with instructions from a selection of fencing schools and styles and able to get through the guard of all but the most skilled of fencing masters and deliver a deadly strike to the heart. The settings can either be manually fixed, or can increase in intensity setting dependant upon the proximity of the intruder, the number of intruders or the length of time the intruder has spent within the field.

The arms themselves are formed of a scale metal skin covering a pneumatic spinal jointed metal core and are highly durable. The arms are fast and can co-ordinate precisely enough to block or deflect incoming projectiles, using their swords to form an intersecting grid to protect their quadrants.

Normally the arms are deployed as a defensive security measure to prevent unauthorised personell from passing through that access point  but, as in the case of the Correr Museum in Venice, they can be used to protect valuable exhibits and displays from theft. Its installation there prevented the vandalism of the artefacts on display on the first floor by members of the God's Mirror sect, although unfortunately the system had not yet been installed in the art gallery on the ground floor and several valuable paintings were lost to the bonfire of the vanities. It was also no defense against the sustained attack of the Chorus, nor the "salvage operation" of the Lemniscate Club.

A well prepared or multi-skilled master thief could bypass the En Guarde system, but it would prove an insurmountable or even lethal obstacle to most cracksmen. The Static Distortion Belts are of use against part of the systems detection devices, but it can prove more dangerous to the wearer, as the En Gaurde Security Post then defaults its heartbeat detector but cannot approximate the dimensions of the body surrounding the heart. This can be a boon to a skilled swordsman whose parries are then not detected or anticipated but it will make sword combats more lethal, no matter what the security level setting, as normally non-lethal blows will be directed through limbs, the body or the head en route to their intended target.

The best method to defeat the security post is to engage the limbs in some form whilst an accomplice either disables the limbs quadrant by quadrant, or if quick enough, slips by them to their goal. A skilled swordsman could potentially lock up all deployed blades (although his senses would have to be sharp enough to detect and engage each potential feint), or a decoy such as a statue could be used to divert attention (although it is likely that the post would engage a target with a heartbeat as a priority).

The En Guarde Security Post remains an eccentric, expensive and somewhat flashy defensive system, but can be lethally effective if deployed effectively against an unprepared intruder. It is certain that whilst there are more immediate and deadly traps in the arsenal of defenses arrayed against the modern criminal, this is one of the succesful deterrents.