Commercial off-the-shelf (COTS) hardware is becoming less and less reliable because of the continuously decreasing feature sizes of integrated circuits. But due to economic constraints, more and more critical systems will be based on basically unreliable COTS hardware. Usually in such systems redundant execution is used to detect erroneous executions. However, arithmetic codes promise much higher error detection rates. Yet, they are generally assumed to generate very large slowdowns. In this paper, we assess and compare the runtime overhead and error detection capabilities of redundancy and several arithmetic codes. Our results demonstrate a clear trade-off between runtime costs and gained safety. However, unexpectedly the runtime costs for arithmetic codes compared to redundancy increase only linearly, while the gained safety increases exponentially.