This software is used for monitoring ethernet networks. It listens on a network interface (without using promiscuous mode) and catches all conversations of MAC address to IP request. It then compares the mac addresses it detected with a pre-configured list of authorized MAC addresses. If the MAC is not in list, arpalert launches a pre-defined user script with the MAC address and IP address as parameters. This software can run in daemon mode; it's very fast (low CPU and memory consumption). It responds at signal SIGHUP (configuration reload) and at signals SIGTERM, SIGINT, SIGQUIT and SIGABRT (arpalert stops itself).