We performed this prospective study to evaluate the efficacy of esophageal detector devices (EDDs), both the bulb and the syringe-type, to indicate positioning of endotracheal tubes (ETTs) in out-of-hospital cardiac arrest patients. Forty-eight adult patients with out-of-hospital cardiac arrest were enrolled. Immediately after tracheal intubation and ETT cuff inflation in the emergency department, the patients were allocated randomly to two cross-over groups. In Group 1 (n = 24), patients underwent a bulb test and a syringe test in sequence. In Group 2 (n = 24), patients underwent a syringe test and a bulb test in sequence. End-tidal carbon dioxide (ETCO(2)) was also monitored. In 56 attempts at tracheal intubation, the bulb, the syringe, and ETCO(2) indicated all eight esophageal intubations. In 48 tracheal intubations, the bulb test correctly indicated 34 tracheal intubations (sensitivity, 70.8%). The syringe test identified 35 tracheal intubations (sensitivity, 72.9%). The results of both tests agreed in 33 tracheal intubations. ETCO(2) was detected in 31 tracheal intubations (sensitivity, 64.6%). No statistical difference was found among the tests. EDDs were less sensitive in detecting tracheal intubation for out-of-hospital cardiac arrest patients. Therefore, proper clinical judgment in conjunction with these devices should be used to confirm ETT placement in these difficult situations.