We examined aspects of social alerting as induced through the presence of an attentive but non-evaluative confederate on mental efficiency. To this end, individuals were administered with a chained mental-arithmetic task (levels: low vs. high demand) in two contextual conditions (levels: alone vs. presence). In addition, we examined self-report measures of subjective state for purposes of control. As a result, the presence (vs. alone) condition improved (not hampered) processing speed (while error rate remained low overall), and this effect was differentially more pronounced for high (vs. low) demand. Reaction-time distributional analyses revealed that improvements in average performance actually originated from a selective speeding-up in the slower percentiles, indicating that social alerting promotes stability of information-processing throughput. These results challenge prevalent theoretical notions of mere-presence effects as individuals became consistently faster and less vulnerable to commit attention failure. Our findings indicate that social presence promotes not only processing speed but volitional steadiness.