We have developed Argus, a novel approach for pro- viding low-cost, comprehensive error detection for simple cores. The key to Argus is that the operation of a von Neumann core consists of four fundamental tasks--control flow, dataflow, computation, and mem- ory access--that can be checked separately. We prove that Argus can detect any error by observing whether any of these tasks are performed incorrectly. We describe a prototype implementation, Argus-1, based on a single-issue, 4-stage, in-order processor to illus- trate the potential of our approach. Experiments show that Argus-1 detects transient and permanent errors in simple cores with much lower impact on performance (4% average overhead) and chip area (17% over- head) than previous techniques.