Background: Snoring is a common complaint that causes significant sleep disruption. Snoring may also increase the risk of vibration-induced vascular injury and potentially carotid plaque rupture and stroke. The upper airway is more collapsible in the supine posture so supine sleep typically worsens snoring. Traditional positional therapy is effective in discouraging supine sleep but treatment compliance is very poor. A new device is designed to be worn on the sternum to monitor sleep position and activate a vibration alarm when supine sleep is detected. A short term crossover trial in positional sleep apnoea patients found the device almost totally abolished supine sleep and showed high patient usage. This device may also be a useful treatment option for positional snorers. Aims: To test treatment effectiveness and compliance with supine avoidance therapy in participants with supine-predominant snoring. Methods: Participants had an in-home sleep study to confirm supine-predominant snoring (supine ≥ 2x non-supine snoring frequency) and to exclude sleep-disordered breathing. Participants were then randomised to either the active or inactive treatment arm (vibration alarm on or off, respectively) with continuous posture logging. During active therapy, the alarm was activated after 5 secs of supine sleep. Participants spent 2 weeks in each arm, and completed an in-home polysomnography study at the conclusion of each arm to establish treatment effectiveness. Overnight supine time, snoring frequency and intensity, and polysomnographic variables were compared between treatment arms via mixed models analysis. Results: Overnight supine time was significantly reduced on active treatment (mean ± SEM 21.8 ± 7.2% to 4.4 ± 2.7%, p < 0.05). Device was worn 100% of all study nights and total device usage per night was high in both conditions (active 7.7 ± 0.3 h vs inactive 7.8 ± 0.4 h). Snoring frequency and intensity remained unchanged in both treatment arms. Conclusion: The new device is highly effective in discouraging supine sleep, and has high treatment compliance. More data are needed to establish treatment effectiveness on snoring frequency and intensity.