Discriminating personally significant from nonsignificant sounds is of high behavioral relevance and appears to be performed effortlessly outside of the focus of attention. Although there is no doubt that we automatically monitor our auditory environment for unexpected, and hence potentially significant, events, the characteristics of detection mechanisms based on individual memory schemata have been far less explored. The experiments in the present study were designed to measure event-related potentials (ERPs) sensitive to the discrimination of personally significant and nonsignificant nonlinguistic sounds. Participants were presented with random sequences of acoustically variable sounds, one of which was associated with personal significance for each of the participants. In Experiment 1, each participant's own mobile SMS ringtone served as his or her significant sound. In Experiment 2, a nonsignificant sound was instead trained to become personally significant to each participant over a period of one month. ERPs revealed differential processing of personally significant and nonsignificant sounds from about 200 ms after stimulus onset, even when the sounds were task-irrelevant. We propose the existence of a mechanism for the detection of significant sounds that does not rely on the detection of acoustic deviation. From a comparison of the results from our active- and passive-listening conditions, this discriminative process based on individual memory schemata seems to be obligatory, whereas the impact of individual memory schemata on further stages of auditory processing may require top-down guidance.