Mobile ad hoc network routing protocols are highly susceptible to subversion. Previous research in securing these protocols has typically used techniques based on encryption and redundant transmission. These techniques prevent a range of attacks against routing protocols but are expensive to deploy on energy-constrained wireless devices. Experience in securing wired networks has demonstrated that, in addition to intrusion prevention techniques, it is useful to deploy intrusion detection techniques as a second line of defense. In this paper, we discuss some of the threats to wireless ad hoc networks, and, specifically, some attacks against the AODV routing protocol. We also present a tool aimed at real-time detection of these attacks. The tool monitors network packets to detect local and distributed attacks within its radio range. Experiments show that the tool provides effective intrusion detection functionality while using only a limited amount of resources.