Horse handlers often encounter problem behaviour resulting from a lack of stimulus control. Handlers are often only 15% of the weight of horses, which evolved strong flight responses. Therefore, many riders and handlers resort to the use of "aids" to maintain control of their animals. However, there are increasing concerns about the efficacy and welfare implication of such devices, particularly when applied to sensitive facial structures. One such device is a Dually® headcollar which aims to increase compliance. Despite its popularity, little is known about the effects of this aid on behaviour or stress. The aim of the current study was to determine whether the use of a Dually headcollar improves compliance during handling and, if so, whether this might be achieved with concomitant increases in stress or discomfort. Subjects completed two novel handling tests, one wearing a Dually with a line attached to the pressure mechanism and one attached to the standard ring as a Control. Crossing time and proactive behaviour were recorded as indicators of compliance. Core temperature and the discrepancy between eye temperatures were measured using IRT before and after testing as an indicator of stress. The Horse Grimace Scale (HGS) was used to measure discomfort caused by each configuration of the device. The Dually did not result in more compliant behaviour, compared to the Control (p=0.935; p=0.538). However, the Dually configuration did result in a significantly higher HGS scores (p=0.034). This may indicate that there is an impact on animal welfare by using this device that is not justified by improved behaviour. However, IRT readings of core temperature (p=0.186) and discrepancy between the eyes (p=0.972) did not indicate the Dually increased stress in subjects. Taken together, this suggests the Dually is ineffective in naïve horses but causes increased discomfort.