Mobile computers are subject to a unique form of denial of service attack known as a battery exhaustion attack, in which an attacker attempts to rapidly drain the battery of the device. In this paper we present our first steps in the design of an intrusion detection system for these attacks, a system that takes into account the performance, energy, and memory constraints of mobile computing devices. This intrusion detection system uses several parameters, such as CPU load and disk accesses, to estimate the power consumption using a linear regression model, allowing us to find the energy used on a per process basis, and thus identifying processes that are potentially battery exhaustion attacks.