This report assesses how standardised communication protocols can enable energy flexibility in household appliances such as heat pumps and white goods at scale. It provides a review of the current landscape of communication protocols and explains the value of establishing a control hierarchy. To support effective and clear requirements, it proposes a matrix framework dividing control into three layers – market signals (layer 1), service instructions (layer 2), and device-specific commands (layer 3) – across a temporal horizon. A review of nascent policy approaches in the UK, California, Australia, New Zealand, Germany, France, and the EU, indicates a fragmented landscape where most jurisdictions address only parts of the protocol stack and only some of the control layers. Using the framework, the report maps the most relevant protocols and assesses their strengths and trade-offs. The report presents a phased roadmap recommending global harmonisation of functional requirements rather than technology mandates.