The safety of patients and staff on acute mental health wards is a significant issue. Safety incidents (self harm, violence, coercion) occur frequently. These cause harm and trauma to patients and staff. We think we can predict when incidents are more likely to occur through real time monitoring of the ward milieu. Intervening early may prevent incidents and social contagion. We have co-designed a monitoring tool which asks patients on mental health wards to input their perceptions of safety into a tablet. This provide real time data on the ward to both patients and staff. The technology interface has been co-designed with people who have lived experience by our design (Thrive by Design) and industry (Ayup) partners and is in open source code. The study used focused ethnography to explore how the technology was implemented on the wards, and routine data to examine its effect on safety.