This report (deliverable 3.4) presents the prototype of the ClimApp-MCH, the personalised and context-specific early warning system that HIGH Horizons will introduce and test in pregnant and postpartum women and in health workers in South Africa, Sweden and Zimbabwe.The prototype was developed by HIGH Horizons partner ULUND and subcontractor TNO, the Netherlands Organisation for Applied Scientific Research. ClimApp-MCH is a smartphone app adapted from ClimApp that was developed and applied in an EU-funded project. ClimApp integrates comprehensive heat stress indices and individual factors to provide a personalized tool to prove heat stress warning and advice when facing extreme heat and cold events. The current version of ClimApp is being adapted to vulnerable groups of pregnant and postpartum women, infants and young children, and to health workers taking care of them. The prototype is therefore provisionally called ClimApp-MCH, thereby referring to maternal and child health (MCH).ClimApp-MCH could play a role as a tool to make heat warnings and advice more accessible for everyone and make people aware of appropriate behaviour during periods with high ambient temperatures.