Implanted satellite transmitters are used in seaducks to track migration routes, breeding, and wintering grounds. However, high mortality rates, handling stress, and inadequate small-scale location data necessitates the use of external transmitters. Three external transmitter attachment techniques were tested, including a Teflon tape harness, sutures to anchor the transmitter through the dorsal vertebral processes, or a 3D individually customized silicon harness on 12 surf scoters (Melanitta perspicillata). Body weight, serum and hematology chemistry, behavioral time budgets, and dive performance were used as measures of impact for each transmitter. Global System for Mobile Communications (GSM) transmitter performance was evaluated for accuracy, precision, and battery performance for use in seabirds. All methods had transient effects on weight, serum chemistry, immune response (sutured transmitters), and increased bottom and total dive times. Teflon harnesses impacted behavior. Silicon harnesses had the least deleterious effects compared to other treatments. Accordingly, we recommend silicon harnesses for deploying external transmitters in wild seaducks.