from web site

Starting with pe in 1933, side judges were changed by the Laurent-Pagan electrical scoring device, with an audible tone and a red or green light suggesting when a touch landed. Foil was automated in 1956, sabre in 1988. The scoring box minimized the bias in judging, and permitted more accurate scoring of faster actions, lighter touches, and more touches to the back and flank than previously.
Each weapon has its own rules and techniques. Equipment needed consists of a minimum of 2 swords, a lam (not for pe), a white coat, underarm protector, two body and mask cords, knee high socks, glove and knickers. Foil The foil is a light thrusting weapon with a maximum weight of 500 grams.

The foil has a little circular hand guard that serves to secure the hand from direct stabs. As I Found This Interesting is not a legitimate target in foil, this is primarily for security. Touches are scored just with the pointer; hits with the side of the blade do not register on the electronic scoring apparatus (and do not halt the action).
Just a single touch can be awarded to either fencer at the end of an expression. If both fencers land touches within a close sufficient period of milliseconds to register 2 lights on the device, the referee uses the rules of "access" to figure out which fencer is awarded the touch, or if an off-target hit has priority over a valid hit, in which case no touch is awarded.
pe The pe is a thrusting weapon like the foil, but heavier, with a maximum total weight of 775 grams. In pe, the whole body is a legitimate target. The hand guard on the pe is a big circle that extends towards the pommel, efficiently covering the hand, which is a valid target in pe.
Hits with the side of the blade do not sign up on the electronic scoring device (and do not stop the action). As the entire body is legal target, there is no concept of an off-target touch, other than if the fencer unintentionally strikes the flooring, setting off the light and tone on the scoring device.