  This letter presents a performance comparison of two popular secrecy
enhancement techniques in wireless networks: (i) creating guard zones by
restricting transmissions of legitimate transmitters whenever any eavesdropper
is detected in their vicinity, and (ii) adding artificial noise to the
confidential messages to make it difficult for the eavesdroppers to decode
them. Focusing on a noise-limited regime, we use tools from stochastic geometry
to derive the secrecy outage probability at the eavesdroppers as well as the
coverage probability at the legitimate users for both these techniques. Using
these results, we derive a threshold on the density of the eavesdroppers below
which no secrecy enhancing technique is required to ensure a target secrecy
outage probability. For eavesdropper densities above this threshold, we
concretely characterize the regimes in which each technique outperforms the
other. Our results demonstrate that guard zone technique is better when the
distances between the transmitters and their legitimate receivers are higher
than a certain threshold.
