Abstract Background and Aims Hospital-acquired infection (HAIs) is a problem for 6-8% of hospitalized patients. HAIs has personal costs, prolongs the hospital stay, increasing the risk of morbidity, mortality, time and staff consuming. Hand hygiene (HH) is essential for preventing infections. World Health Organization (WHO) recommends hand hygiene compliance (HHC) as a key performance indicator. Manual observations of HHC are time consuming and may affect compliance by the physical presence of the observers (Hawthorne effect). There is a need to identify the most effective long-term intervention to improve HHC and reduce HAI. The Danish Ministry of Health have chosen blood stream infections (HA-BSI) as a national indicator for the overall risk of HAIs expecting an incidence of no more than 8 cases per 10,000 patient days. The aim of the present study was to examine the use of an automated sensor technology to improve HHC and prevent HAIs in an inpatient department for nephrology and intern medicine. Nephrology patients have a high number of invasive catheters, which may increases the risk of HAI. Method The study comprised a 2 year cohort with no specific HHC interventions (July 2018-June 2020), a baseline period (February 2020-June 2020) to investigate HHC level by an electronic hand hygiene measuring system (EHHMS) without ongoing HHC interventions followed by a 3 year cohort period (July 2020-June 2023) with various EHHMS-based feedback interventions to staff. Intervention consisted primarily of group feedback and later individual feedback. All caregivers and doctors carried an anonymous Sani ID tag (Sani Nudge, DK) fixed to their nametag throughout the study period. EHHMS-based Sani Sensors were located in designated locations in the clinical department with the purpose of continuously capturing the caregiver patient contact including staff use of liquid alcohol based hand rub (ABHR). In Denmark, the national hygiene guidelines also require that ABHR follow hand wash. Local hygiene mentors regularly presented anonymous group data on boards and in letters to the staff. Soon after there was a demand on individual data, which was then added by individual results forwarded in a personal email every week. HA-BSI was defined as the presence of a pathogen in the blood and the prescription of an appropriate concomitant antimicrobial treatment and classified as hospital-acquired if the patient has been hospitalized for >48 hours. Data were obtained from various electronic health care systems in the hospital. Results We collected HHC data by monitoring 203 caregivers and 50 doctors for a period of 40 months. Caregivers HHC improved after implementation of an electronic hand hygiene measuring system from baseline to group feedback and finally individual feedback (39% vs 50% vs 71%). For doctors, the improvement from baseline to group feedback and finally individual feedback was 30% vs. 32% vs 52%. The overall improvement curve reached a stable plateau after 20 months. An incidence rate of 14 HA-BSI cases per 10,000 patient days during a previous two years control period (95% CI 8.8-21.2) was during the intervention period markedly reduced to 5 HA-BSI cases per 10,000 patient days (95% CI 2.3-9.0). This difference was statistically significant, P = 0.004. Conclusion The use and feedback of the electronic hand hygiene monitoring system improved successfully hand hygiene compliance in the groups of both caregivers, doctors, and furthermore reduced the rate of HA-BSI significantly. We observed a significant stepwise increase in compliance after group feedback data and later after reporting individual data. There continue to be a need to find effective long-term interventions to improve and keep a high level of hand hygiene compliance and a sustained reduction in hospital-acquired bloodstream infection.