Objectives: Poor sleep hygiene behaviours lead to poor mental and physical health, including weight gain, increased chances of cardiovascular disease, depression, and anxiety (NHS, 2018, Woods & Scott, 2016). Mobile phones produce radiation and blue light, both of which disturb sleep and reduce sleep quality by suppressing the production of melatonin. The aim of this study was to investigate how proscriptive and prescriptive message frames and heteronomy- and autonomy-framed implementation intentions impact night-time phone use. Method: Two hundred and thirteen participants (68.1% female) were randomised into one of six conditions and completed two online questionnaires one week apart. Participants read a message (proscriptive-frame vs. prescriptive-frame), and then wrote out their plans to carry out behaviour change (heteronomy-frame vs. autonomy frame vs. control). Questionnaires measured the following: General Sleep Hygiene, Night-time Phone Use, Psychological Reactance, Intentions, Perceived Behavioural Control (PBC), Attitudes, Consideration for Future Consequences (CFC), and Self-Efficacy. The study employed a 2 (Message Framing: Prescriptive, Proscriptive) x 3 (Implementation Intention: Autonomy vs Heteronomy vs Control Group) experimental between subjects’ design. Results: ANCOVAs found no significant main effects of message framing (proscriptive, prescriptive), implementation intentions (autonomous, heteronomous), or an interaction between both on night-time phone use. Conclusion: Despite insignificant results, this study contributes to the large gap in the literature as well as providing potential practical implications. Strengths, limitations, and recommendations for future research are discussed,