Recently, alarm systems have become more sensitive and ubiquitous. Unfortunately, sensitive alarm systems may produce greater numbers of false alarms, lowering an operator’s level of trust and degrading task performance. In the past, researchers have considered only situations where individuals react to alarms. Because of the frequency and variability of teamed alarm reaction scenarios, we investigated the reactions of independent and dependent teams to collateral marginally reliable alarms. Based on prior literature, we expected dependent teams to show slower but more appropriate alarm reactions and poorer ongoing task performances. Eighty general psychology students (40 two-person teams) independently or dependently performed a psychomotor task while reacting to two alarm systems; one that was 80% reliable, and one that was 40%, 60%, or 80% reliable. Participants responded more frequently to alarms of higher reliability, and less appropriately to those of medium reliability. Generally, dependent teams made more appropriate alarm reactions. Our results suggest that designers and trainers should promote team interdependence and communication when operators are faced with marginally reliable signals.