Abstract-Mobile wireless handheld devices can support ad hoc communication when infrastructure systems are overloaded or not available. Unfortunately, the constrained capacity of their batteries and the energy inefficiency inherent to the ad hoc communication poses a challenge causing a short lifetime. Protocols and application layer services, such as security, can be designed (offline) to do an efficient use of the resources. Realtime adaptation can further minimise their impact on the energy consumption, increasing the network lifetime thus extending the availability of network communication.In this paper, we propose an energy-aware adaption component for an Intrusion Detection System (IDS) in mobile ad hoc networks (MANET). The component is in charge of adjusting the parameters of the IDS based on the current energy level, using the trade-off between the node's response to attacks and the energy consumption induced by the IDS. The approach is based on a model for accounting CPU energy consumption in network simulation, which has been implemented in an existing IDS in ns-3. Simulations demonstrate that the adaption has a positive impact on the battery life time, increasing it by 14%, without deteriorating the network-wide performance of the IDS.