Active and potentially hazardous volcanoes in East Africa (Tanzania, Kenya, Ethiopia) are not currently monitored on a regular basis. Among the most active ones, Oldoinyo Lengai has been almost continuously active since 1983. Activity has been confined to small-scale effusive and explosive eruptions of low temperature (~550°C) natrocarbonatite within the summit crater. Historical eruptions’ accounts illustrate that Oldoinyo Lengai also repeatedly displays much more explosive (i.e. violent strombolian or sub-plinian style) eruptions of silicate magma. Daily MODIS images offer a low-cost route to monitor volcanic thermal activity. Existing methods applied on a worldwide scale, such as the MODVOLC algorithm developed by the University of Hawaii, are insufficiently sensitive to monitor small-scale thermal anomalies. MODLEN is an adapted semi-automated algorithm, using MatLab, which allows daily record of the thermal emission at Lengai and the identification of high intensity activity. MODLEN is calibrated and validated using the activity reports from field visits. Despite the small-scale and low temperature of the eruptive activity at Lengai, MODLEN is able to detect all periods of increased activity observed in the field. A 5-year time-series dataset, resulting from analysis of more than 2500 night-time MODIS scenes, has been acquired as a baseline for future near-real time monitoring. It provides insights on the factors controlling the temporal distribution of high intensity activity events. Improvement of the method, to avoid false detection due to partial cloud coverage and detection of the full extent of thermal alerts are also discussed. Although recent activity has been moderate at Lengai, a more intense explosive eruption is overdue. Monitoring is needed to try and anticipate the transition to more hazardous eruption styles and to gain insights into the controls on eruption intensity at Lengai.